CR 311 AU Preliminary Field and Laboratory Testing Discussion

Week 3 – AssignmentThe Difference Between Preliminary Field and Laboratory
Testing
[WLOs: 1, 2, 4] [CLOs: 2, 3, 4, 5]
Handling and processing evidence is an integral component of crime scene management because it lays the
foundation for everything the court must consider when weighing the admissibility of evidence. For the most part,
the courts prefer testing being carried out in a laboratory setting. However, there are exceptions, such as times
when an initial examination also yields valuable information. In this assignment, you will differentiate between
testing that might be done on-scene versus in the laboratory, identify testing that might be subject to preliminary
testing, as well as compare the different results yielded by preliminary field versus laboratory testing. Support
your assignment with examples from this week’s required material(s) and/or a minimum of three other scholarly
or credible resources and properly cite any references.
Prior to beginning work on this assignment, please review the following:
• From the text:
◦ Chapter 8: Pattern Evidence 1: General Patterns and Fingerprints
◦ Chapter 9: Pattern Evidence 2: Firearms, Tool Marks and Document Analysis
• From the free, downloadable resource at the web page Crime Scene Investigation Guide
(https://www.nfstc.org/products/crime-scene-investigation-guide/) :
◦ Section D – Completing and Recording the Crime Scene Investigation
◦ Section E – Crime Scene Equipment
• The articles:
◦ An Automated Approach to the Classification of Impact Spatter and Cast-Off Bloodstain Patterns
◦ Chemical Enhancement of Footwear Impressions in Blood Recovered from Cotton using Alginate
Casts
• From the free PDF copy at the web page Strengthening Forensic Science in the United States: A Path
Forward (2009) (https://www.nap.edu/catalog/12589/strengthening-forensic-science-in-the-united-states-apath-forward) :
◦ Section 10. Automated Fingerprint Identification Systems
◦ Section 11. Homeland Security and Forensic Science
• The video Forensic Science: Analysis of Drugs Using Colour Tests
(https://www.youtube.com/watch?
v=hXh8pMvc3-o) shown above
• From the video Bodies, Blood, and Ballistics: Forensics School, Part One:
◦ Segment 2. Forensics: Blood Spatter 02:35
◦ Segment 5. Blood Spatter and Trajectories 04:35
• From the video Hands-On Police Work: Forensics School, Part Two:
◦ Segment 3. Crime Scene Photography 02:27
◦ Segment 6. How to Capture and Record Fingerprints 03:10
◦ Segment 8. Crime Scene Documentation 03:18
You are also strongly encouraged to review the list of recommended resources, as they may assist you with this
assignment.
In your paper, address the following:
• Identify what types of evidence might be subjected to preliminary or field testing.
• Describe at least two types of testing that might be done on scene.
• Differentiate between why some evidence can and should be subjected to preliminary testing on scene, while
other types should not.
• Explain how the on-scene test compares to laboratory testing.
• Compare and contrast the results yielded by preliminary field versus laboratory testing.
• Compare and contrast the admissibility of on-scene versus laboratory testing at trial.
The Difference Between Preliminary Field and Laboratory Testing paper
• Must be 750 words in length (not including title and references pages) and formatted according to APA style
as outlined in the Ashford Writing Center’s APA Style (http://writingcenter.ashford.edu/apa-style) .
• Must include a separate title page with the following:
◦ Title of paper
◦ Student’s name
◦ Course name and number
◦ Instructor’s name
◦ Date submitted
For further assistance with the formatting and the title page, refer to APA Formatting for Word 2013
(http://writingcenter.ashford.edu/apa-formatting-word-2013) .
• Must utilize academic voice. See the Academic Voice (http://writingcenter.ashford.edu/academic-voice)
resource for additional guidance.
• Must include an introduction and conclusion paragraph. Your introduction paragraph needs to end with a
clear thesis statement that indicates the purpose of your paper.
◦ For assistance on writing Introductions & Conclusions (http://writingcenter.ashford.edu/introductionsconclusions) as well as Writing a Thesis Statement (http://writingcenter.ashford.edu/writing-a-thesis) ,
refer to the Ashford Writing Center resources.
• Must use at least three scholarly, peer-reviewed, and/or credible sources in addition to the course text.
◦ The Scholarly, Peer-Reviewed, and Other Credible Sources
(https://content.bridgepointeducation.com/curriculum/file/e5359309-7d3c-4a21-a41044d59303ccef/1/Scholarly%20Peer-Reviewed%20and%20Other%20Credible%20Sources.pdf) table offers
additional guidance on appropriate source types. If you have questions about whether a specific source is
appropriate for this assignment, please contact your instructor. Your instructor has the final say about the
appropriateness of a specific source for a particular assignment.
◦ To assist you in completing the research required for this assignment, view this Ashford University
Library Quick ‘n’ Dirty
(https://ashford.mediaspace.kaltura.com/media/Ashford+University+Library+Quick+%27n%27+Dirty/0_bcsbcjee)
tutorial, which introduces the Ashford University Library and the research process, and provides some
library search tips.
• Must document any information used from sources in APA style as outlined in the Ashford Writing Center’s
Citing Within Your Paper (http://writingcenter.ashford.edu/citing-within-your-paper) guide.
• Must include a separate references page that is formatted according to APA style as outlined in the Ashford
Writing Center. See the Formatting Your References List (http://writingcenter.ashford.edu/format-yourreference-list) resource in the Ashford Writing Center for specifications.
Consider using Q for your library research and to access writing supports, and tutoring services available to you.
See the Guide to Installing and Using Q
(https://content.bridgepointeducation.com/curriculum/file/dd00f7497449-469c-9bd3-1e6e269bd895/1/Guide%20to%20Installing%20and%20Using%20Q%20for%20Success.pdf) for more
information.
Carefully review the Grading Rubric (http://au.waypointoutcomes.com/assessment/25747/preview) for the
criteria that will be used to evaluate your assignment.
Waypoint Assignment
Submission
The assignments in this course will be submitted to Waypoint. Please refer to the instructions below to submit
your assignment.
1. Click on the Assignment Submission button below. The Waypoint “Student Dashboard” will open in a new
browser window.
2. Browse for your assignment.
3. Click Upload.
4. Confirm that your assignment was successfully submitted by viewing the appropriate week’s assignment tab
in Waypoint.
For more detailed instructions, refer to the Waypoint Tutorial
(https://content.bridgepointeducation.com/curriculum/file/dc358708-3d2b-41a6-a000-
ff53b3cc3794/1/Waypoint%20Tutorial.pdf)
(https://content.bridgepointeducation.com/curriculum/file/dc358708-
3d2b-41a6-a000-ff53b3cc3794/1/Waypoint%20Tutorial.pdf) .
This tool needs to be loaded in a new browser window
Load Week 3 – Assignment in a new window
Pattern Evidence I:
General Patterns and
Fingerprints
8
Franz12/iStock/Thinkstock
Learning Outcomes
After reading this chapter, you should be able to
• Describe pattern evidence that can be used for identiϐication, individualization,
and reconstruction.
• Explain the collection and preservation of pattern evidence.
• Explain how pattern evidence is analyzed.
• Summarize the nature and history of ϐingerprints and their role in personal
identiϐication.
• Discuss how ϐingerprint evidence is collected and preserved.
• Explain how ϐingerprints are analyzed.
Introduction
In this chapter and in Chapters 9 and 10, we will discuss pattern evidence. As we mentioned in Chapter 1, identiϐication, individualization, and reconstruction can
be major aspects of a forensic case or a forensic investigation. Many of the topics in the next two chapters concern patterns for individualization, including physical
patterns, ϐingerprints, footprints, footwear and tire impressions, handwriting, ϐirearms and tool mark identiϐication, and bite marks. Bloodstain patterns are
reconstruction patterns, and we discuss this topic in Chapter 10.
This chapter looks closely at physical patterns (broken or torn objects) and ϐingerprints (a major category of individualization pattern).
Pattern evidence can be very important in an investigation, because it includes many types of evidence familiar to most people. Some types of patterns can
potentially be individualized—that is, attributed to a speciϐic source. In this way people can be associated with or dissociated from speciϐic places, like scenes, or
from other people. Conclusions from pattern evidence comparisons are usually more deϐinitive than those from trace or chemical evidence—and correspondingly
more useful to juries and judges. Pattern evidence is examined by the eye, for the most part. No complicated instruments, other than the occasional use of
microscopes, are required. Sometimes a pattern evidence match can be obvious to anyone, such as in a physical pattern match (jigsaw ϐit), making the evidence
easier to present to a court.
8.1 Classi ication of Pattern Evidence
Pattern evidence can be classiϐied into three overarching categories: patterns for identi ication, patterns for individualization, and patterns for reconstruction. This
idea follows by analogy from the three activities that can make up the elements of a forensic investigation—identiϐication, individualization, and reconstruction—
that we discussed in Chapter 1. So, just as we can talk about identiϐication, individualization, and reconstruction as elements of a criminalistics investigation, so
can we talk about pattern evidence categories that have these elements as their goals.
Identiϐication (or classiϐication) patterns, which are used to identify things in our everyday environment by general shape and form, are applied in forensic work
to hair comparisons (Chapter 6) and handwriting (Chapter 9). The different individualization patterns that are important in forensic work are discussed in detail
in this and the next chapter. In later chapters, we brieϐly discuss some reconstruction patterns, including bloodstain patterns. Before speciϐic types of physical
patterns are discussed, let’s go over each category of pattern evidence.
Patterns for Identi ication
Patterns for identiϐication are used to identify objects and people in our everyday life and experience. For instance, right now, you might be sitting at a table. How
do you know it’s a table? You might say, “I know it’s a table just by looking at it.” The reasoning behind your knowledge is that your brain has a record of the
pattern of a table, which you learned when you were younger. This pattern has to do with the shape and form of a table: its four legs and ϐlat top. There are
variations of tables in the world, but on the basis of their general pattern, we classify them all as tables. When you see this particular pattern, it matches up with
the brain pattern that identiϐies it as a table. This works the same way for facial recognition. You recognize people you know instantly—even in a large crowd and
even if you haven’t seen them in a long time. But what if one of your friends tries to describe someone new to you in enough detail for you to ϐind this stranger in a
crowded place, like an airport? No matter how much detail is provided, you may not ϐind him or her. It is very difϐicult to enumerate the features and properties of
a person’s facial pattern that one person recognizes in enough detail to allow someone else to do so.
The human mind is very good at pattern recognition, but it is not yet clear in a detailed way how it works. In forensic work, the examinations that most closely
resemble this type of pattern are hair comparisons and handwriting comparisons. In comparing hairs or handwriting samples, the examiner looks at speciϐic
features in the known and the questioned sample. But the comparison is more than just a checklist of which features match. The examiner incorporates the sum of
all these feature comparisons into an overall pattern comparison between the questioned and known. It is a lot like the facial recognition example. Recognizing
someone’s face is more involved than a simple checklist of the features that are compared. One of the important things that distinguish handwriting and hair
comparisons from the other evidence category comparisons is intraindividual variability, which means that there is variability in the knowns themselves, and this
must be taken into consideration in the comparison. One could argue that handwriting or hair comparisons fall into the individualization pattern category.
Similarly, face recognition of a speciϐic person involves an individualization pattern comparison.
Patterns for Individualization
Patterns for individualization are characteristic of evidence that can be unique among the members of their class. This can be very important associative evidence
in an investigation. We might be able to ϐigure out that a particular tire made a tire mark, that a particular piece of footwear made an impression, or that broken
pieces of a headlight lens came from a speciϐic car in a hit-and-run, which may tie a suspect vehicle to the scene of a crime. There are two major types of
individualization patterns: physical match patterns and impressions.
Physical Matches
Physical match patterns are formed from the pieces of randomly broken objects and are sometimes called “jigsaw ϐit” matches. The patterns are like a picture
puzzle. For instance, if a glass was broken and there weren’t too many pieces, it wouldn’t take long to ϐigure out how the pieces ϐit back together to form the
original glass. Even if some pieces were missing, it would be likely that at least a few pieces would ϐit together. Note that this works for solid objects that fracture
in a random fashion. In cases of solid objects, these physical matches are also known as fracture matches.
Suppose that several pieces of a broken glass were found at a crime scene. Later, a suspect was developed, and police searched his apartment. In the cuff of a pair
of pants, a piece of glass was found. The lab performed an analysis and physically matched the pants-cuff piece to the glass pieces from the scene. This evidence
goes a long way toward putting the owner of these pants at the scene around the time the glass was broken.
Think About It
In the previous example about the suspect and the piece of broken glass, are you convinced that this evidence places the suspect at the scene around the
time the glass was broken? What if you were an expert witness and the suspect’s lawyer asked, “How do you know glasses break randomly? Why couldn’t
there have been another glass in my client’s kitchen that broke in a way that produced the piece the police found, and it just happened to ϐit the scene
pieces?” How would you answer the lawyer’s question? How would you prove that glass breaks randomly and show that this is really an individualization?
Is this something that can be proven?
When the object that fractures is solid and breaks in a random fashion, the physical matching of the pieces is called direct, or sometimes primary. If an object or
item isn’t solid or fractures in a way that doesn’t result in clean, smooth fracture surfaces—such as pieces of cut or torn fabric or a snapped piece of wood with
ragged irregular ends—the physical match is called indirect, or secondary. Experts can work to try to ϐit these pieces back together, but even if the match looks
right, there is uncertainty. It is much easier to imagine a piece of similar cut or torn fabric “matching” an unknown by chance than it is in the broken glass case.
Experts will not generally say that secondary physical matches are true individualizations. Instead, they might say the pieces ϐit and are consistent with having
been part of the same original, but they cannot conϐirm a common origin.
Impressions
Another major type of individualization pattern is impressions. Impressions occur
when two objects come in contact with one another and one object leaves behind
distinguishing markings on or in the other. There are three types of impressions, which
are distinguished based on depth and how the marks are made. Impressions that are
essentially stamped by an object into or onto another are called imprints if they are
more or less ϐlat (two-dimensional). They are called indentations if they have depth
(three-dimensional character). For example, many ϐingerprints and tire impressions
are imprints because they are left on hard surfaces. However, they can be indentations
if they are left in a soft receiving medium, such as a ϐingerprint in soft tar or a tire
impression in soft soil. If the receiving surface is marked by an object or surface
moving across it—in effect, being scratched by it—the marks are called striations. The
markings on bullets that ϐirearms examiners use to identify the gun from which a
bullet came are striations. Any sliding tool mark, like a mark made by a screwdriver
scraping across a latch plate on a door, is also a striation.
Patterns for Reconstruction
Patterns for reconstruction help create theories of the events that occurred at a scene.
Reconstruction patterns include glass fractures, furniture and objects at a scene,
tracks, trails, trajectories of projectiles, skid marks in auto accidents, and more.
Fracture patterns in glass can help determine what caused the breakage. The
distribution and condition of clothing and objects at scenes can help determine what
happened, if there was a struggle, movements of persons involved, and so forth. Tracks
and trails can help show the direction of movement of people. Projectile trajectories,
such as the path followed by a bullet in a shooting case, can help reconstruct the
position of the weapon with respect to the target. Skid marks help automobile accident
reconstruction specialists determine the direction and speed of vehicles just prior to
an accident. Depending on the speed and direction of a vehicle at the time its brakes
are applied, a tire skid mark with a particular length and direction is created.
Documentation and measurements of the marks can help reconstruct direction and
speed. There are computer programs now that assist trafϐic accident reconstruction
specialists in these tasks.
Alexandre Meneghini/Associated Press
Bullet striations leave distinct impressions that can be used to match
them to the gun from which they were shot. What are some other
examples of striations?
8.2 Collection and Preservation of Pattern Evidence
There are different ways of collecting pattern evidence, depending on the markings or impressions left behind. Two important terms to know are positive and
negative impressions. A positive impression is identical to the object that made it, whereas a negative impression is its mirror image. The shoe prints left in the
mud are negative impressions; they are negatives of the shoes’ soles. In this scenario, the positives would be the shoes’ soles. The same is true in the case of a tire
indentation. This mark would be collected by casting. The resulting cast is a positive, like the tire that made the mark, so the cast can be compared to the tire.
In general, imprint markings are collected by ϐirst photographing the mark with and without a scale
present, and then either collecting the whole object that has the mark, or if that is not possible, by tapelifting. If the imprint markings are made up of dirt or grease or other residues, they can be lifted from a
surface with sticky tape (similar to Scotch® tape). The tape must be placed onto the surface with care,
to avoid creating any bubbles. A rubber roller can help in this process. Then the tape is carefully lifted,
so as to avoid any damage to or distortion of the mark, and placed onto a contrasting backing surface. A
black mark, for example, would be placed onto a white backing surface. This item is then labeled with
the usual required information and placed into a paper or plastic container and sealed. Lifting tapes of
various sizes and appropriate backings are commercially available.
Indentation markings must also be photographed. As mentioned in Chapter 2, side lighting can help
give the impression better contrast. After photography, the mark is cast. For this purpose, dental stone
is used. This is a special ϐinely ground plaster used by dentists to make molds for restorations. It is
mixed with water to make a pancake-batter-consistency mixture, then poured into the indentation so
as not to disturb any of the detail present. Once it hardens, it can be removed. It captures ϐine detail
quite well. In addition to labeling the packaging of a cast, the collector can scratch a case number or
item number into the top side of the hardening dental stone. There are special types of casting
materials for tool marks, marks in snow, and other speciϐic types of marks. Tool marks are discussed in
a later chapter, but for now, dental stone is not capable of capturing the very ϐine detail in a tool mark
(like a striation mark made by a screwdriver on a lock plate). There are silicone-based materials
commercially available that are better suited for this task. These silicone-based materials can also be
used for indentation-type ϐingerprints, such as a ϐingerprint in wax. Indentation markings in snow pose
a problem because dental stone gives off heat as it hardens, and the heat can melt the snow and destroy
the impression detail. Products like Snow Print Wax can be sprayed onto the mark to protect it from
this effect. An indentation impression is a negative, and so the cast of the impression is a positive.
Accordingly, the cast can be compared directly with the tire or footwear or other item that is thought to
have made the indentation.
Both in collecting evidence and in thinking about how pattern comparisons are done, it is important to
remember that comparisons must be made between like impressions—left with left, right with right,
positive with positive, and negative with negative. The detailed individual characteristics that help in
individualizing the mark must be in the same orientation as the original object that made the mark (or
as its mirror image). Sometimes this requires that the lab create a known from the suspected item in
order to make the comparison. For example, a lifted footwear impression from a scene would be
compared with an inked impression of the suspected footwear made in the laboratory.
Johner/SuperStock
Snow prints are among the most dif icult indentation
markings to collect and preserve. Can you think of any
other environments where pattern evidence would be
particularly hard to obtain?
Think About It
Imagine you are a pattern evidence examiner, and the police bring you a tape-lifted impression of a tire they have gotten from a ϐlat concrete surface. They
have a suspect car, but it is up to you to ϐigure out how to compare the tires with the impressions. How would you make the known specimens from the
tires to use for comparison with the questioned impression?
8.3 Analysis of Pattern Evidence
In Chapter 1.4 class and individual characteristics were introduced. These concepts become very important in physical pattern analysis. Consider items like shoes
or tires. There are hundreds, or maybe even thousands, of basically identical shoes and tires in the world. They were manufactured under quality control
standards to be as similar as possible. So if a brand­new shoe or tire leaves an impression, what characteristics make up that impression? Class characteristics.
With a new shoe, the sole pattern, manufacturer, size, type of shoe, and so forth, can be determined. However, it is impossible to distinguish any individual shoe in
that class, because there are not yet any individual characteristics. The same rule applies to tires. Individual characteristics come about as a result of wear. Sole or
tire pattern features wear down in nonuniform ways, parts of the sole or tire can be cut or torn by wear, foreign objects can make unusual marks in the sole or tire
material, and so on.
The forensic examiner will make a comparison between a questioned mark and a known object. If you recall, questioned objects are found at the scene and have
an unknown source. Known objects have a known source and can help determine the source of a questioned object. Here, the matter of questioned and known
specimens becomes a little more complicated with the inclusion of positive or negative impressions. A sneaker sole itself, for instance, cannot be compared with
the impression mark because positives and negatives cannot be compared directly. The features of interest would be mirror imaged. Take a good look at Figure
8.1.
Figure 8.1: Sneaker sole impressions
Analysis of pattern evidence, such as this sneaker sole, requires that the correct type of impression (positive or negative)
and orientation be used to make a comparison between the unknown and the known mark.
Adapted from Spantomoda/iStock/Thinkstock
The igure shows a left sneaker, but it is a mirror image with respect to the inked impression on the brown paper. To make a comparison, the sneaker must be used
to make a known negative impression. This might be an inked impression on paper or on transparent plastic. These are good surfaces for capturing the detail in
the footwear in approximately the same way as it was captured in the evidence mark. Note that these inked impressions would be made by someone actually
wearing the sneaker and taking a step, so that there would be weight on the shoe. The middle impression on transparent plastic in Figure 8.1 is turned to match
the orientation of the sneaker in the picture, but if it is turned over, it will match the orientation of the paper print. As an inked sneaker impression, it is a negative
and therefore could be used as the known for an unknown imprint thought to have been made by that sneaker. You can also see from Figure 8.1 how it would be
easy to confuse left and right if you don’t keep track of what you are doing when making these impressions on transparent surfaces.
Physical Matches
There are four criteria that must be met in order to state that evidence is individualized in a fracture match. The criteria include the following.
1.
2.
3.
4.
The objects must be broken, torn, or cut.
They must be capable of being realigned.
There must be a jigsaw it (or lock­and­key it) surface to surface.
The match must be unique.
With indirect or secondary matches, such as torn fabrics, it is unlikely that individuality can be declared, even if the pieces appear to it. It isn’t intuitive that every
fabric cut or tear will be completely random and thus unique. This means that there is a possibility of a chance duplicate. Two different cuts, or even tears, of a
fabric could be so similar as to be indistinguishable in a comparison.
Physical matching is done by the eye or with the aid of a magni ier or stereo microscope. This is a microscope with two eyepieces (enabling stereo vision) that is
essentially a magni ier. This type of matching is intuitive and quite familiar to people. As a result, it is very convincing for a jury or judge, because they can look at
it and see it for themselves. This can be dangerous, however, because if an expert overinterprets a match, there is a better chance the jury will believe him or her.
Impressions
With the other impressions that have been discussed, such as those from shoes or tires, the comparison is more subjective and will depend on the examiner’s
training and experience. These comparisons are also done by the eye or with the aid of simple magni iers. The individual characteristics must be located and their
position within the overall pattern noted. With experience, examiners develop a sense of what the different individual characteristics are in each impression. They
also learn to judge the quality of the impression and how many individual characteristics it possesses. As you can imagine, not every impression gives good detail.
It might be light, smudged, or distorted. Examiners use these factors to determine if known and unknown markings match. There is no rule about how many
matching individual characteristics must be present to declare that the known is the source of the questioned. This determination is up to the examiner and is
thus more subjective. Unlike a physical match, these comparisons are not intuitive or obvious, and the skill to do them comes only from extensive training and
experience.
As with the random fracturing of solid objects, individuality due to wear comes about because the accidentals, the individual characteristics acquired by the item,
are expected to be random. With a sneaker sole, for example, this might be a cut or a particularly worn area. An examiner must use his or her training and
judgment to assess the quality of the impression and the number and distribution of individual characteristics that were transferred to the mark from the object.
These factors help the examiner decide what conclusion to draw from the comparison.
Other patterns can fall into this general category. Occasionally, a lip print or ear print is examined. These imprints are unusual, so there is not much examiner
experience with or research on them. Thus, there is not much of a basis for inding enough individual characteristics to reach an unambiguous conclusion. Sock
prints or glove prints may be included here, as well as fabric impressions, such as when a blood­soaked fabric is pressed against a nonabsorbent surface and
leaves an impression in blood. Sometimes, in a hit­and­run case, the pattern of the fabric from the clothing of a victim can be impressed into the bumper of a
vehicle.
Bite marks can be included here, as well. Only forensic odontologists deal with bite
mark comparisons, but these marks can be considered members of the patterns for
individualization category. Bite marks are complicated because different numbers of
teeth might make them, they are frequently on curved surfaces that can change or
shrink, and it is dif icult to prepare truly proper knowns for comparison from a
suspect’s teeth. One can make models (casts) of someone’s teeth, but it is not easy to
reproduce the evidentiary mark, because they are usually on living skin and the
surfaces are often curved. Up until around 10 years ago, forensic dentists sometimes
declared that a bite mark could be individualized and could identify a particular
person. There were a number of cases in which bite mark evidence igured in a
criminal conviction.
One famous example of these cases occurred in the Florida trial of the serial murderer
Ted Bundy. Bundy was one of the most proli ic serial murderers in U.S. history. He is
known to have killed dozens of women in Washington, Oregon, Idaho, Utah, Colorado,
and Florida, and investigators familiar with him think there were many others. His
entire story is long and complicated, but the bite mark evidence against him came in
the murder of two Chi Omega sorority sisters and the assault on two others in their
sorority house at Florida State University in January 1978.
Two forensic odontologists testi ied that the bite marks on the murdered women were
from Bundy. Bundy was executed on January 24, 1989. Leading up to his execution, he
talked to investigators from several of the western states where he had lived; he
confessed to a long list of murders, some of which the police hadn’t even known about.
He was such a skilled liar, however, that police could never be sure how many victims
there really were.
Associated Press
Bite mark evidence is not as accepted today as it was during Ted Bundy’s
trial. Do you think the case’s outcome might have been different if bite
marks were considered circumstantial evidence?
However, recently, the tide has turned against bite mark evidence. A 2009 report by the Committee on Identifying the Needs of the Forensic Sciences Community
was highly critical of the discipline, inding that “the scienti ic basis is insuf icient to conclude that bite mark comparisons can result in a conclusive match” (p.
175). An investigation by the Washington Post published in 2015 came to the same conclusion, bringing forward two cases in which people were accused of
murder based on bite mark evidence (Balko, 2015). In these cases, later DNA typing of saliva around the bite mark on the victim showed that the saliva did not
match the person whom the forensic odontologist had positively identi ied. Also in 2015, the White House Of ice of Science and Technology Policy called for bite­
mark analysis to be abandoned, as it did not have a strong scienti ic basis (Augenstein, 2015). Due to this accumulation of evidence, bite marks are not generally
attributed to a speci ic person anymore. It is more likely that a dentist will say either that the person is excluded or could not be excluded.
Think About It
Bite marks are no longer considered a way to speci ically identify someone, but they can be used to exclude or include a person of interest. Do you think
that if Ted Bundy were on trial today, the bite marks would still be a key piece of evidence against him? If you were the odontologist testifying in the trial,
how would you explain the bite marks to the court? What language would you use to indicate that you thought he was probably the biter but that there
wasn’t any scienti ic way to really establish that fact?
Individualization
The term individualization has been used frequently in this discussion. The term means uniqueness—the only one, to the exclusion of all others. Recently, there
has been discussion among pattern analysts about whether uniqueness is a realistic conclusion based on their knowledge of and experience with many of these
patterns. How is anyone sure there is no chance duplicate anywhere? There has been a trend in the direction of changing the terminology to describe persuasive
matches as a single source (Polski et al., 2011). If a phrase like attributable to a single source were to be used and de ined in an understandable way that suggested
a strong possibility of individuality or common origin but permitted some uncertainty, it could be a better re lection of the state of knowledge. Experiments on
pattern matching will continue, but in truth there is no way to compare any given pattern with every possible source. Even if a single pattern were studied—for
example, a striation tool mark made by a screwdriver on a scratchable surface—it is nearly impossible to replicate. The angle, the pressure, the speed of
movement—these could all affect the appearance of the inal mark. And that is only in one surface! So we have to rely on the scienti ic concept of induction. If we
have good information on basic principles about a representative number of possible situations, we can, by inductive logic, extend them to cover all the marks in
that category.
8.4 Fingerprints
Among the oldest and best established individualizing markings, ingerprints remain one of the most important types of physical evidence in the repertoire. A
ingerprint impression from a scene matched to the known ingerprint of a suspect essentially proves that the person was there at some point. Almost everyone
believes that ingerprints are highly individual. It has become part of our unspoken culture. People talk about “DNA ingerprinting” and use the term unique to
describe a ingerprint.
Fingerprints are a form of biometric identi ier, a biological measurement or feature of a person that has the potential of being used as the basis for
individualization. Other types of biometric identi iers include DNA; facial features; parts of the eye, such as retinas and irises; and even handwriting.
There is interest in biometrics as individuality markers because they are dif icult to reproduce or forge. All documentary identi ication systems have been subject
to forgery, including driver’s licenses, passports, credit and debit cards, and employee identifying cards or badges, making it possible for a criminal to change his
or her identity. This is more dif icult and less common with biometric markers.
Fingerprints are an attractive biometric because they are formed during a person’s development in the womb, are permanent and unchanging throughout life, are
easy to record and scan unobtrusively, and involve a bare minimum of privacy invasion to record. Something to remember about the use of ingerprints as
biometric identi ication vehicles is that the goal is not to individualize the person among everyone in the world. That is not necessary. A system might be put in
place to distinguish employees who work in a large, secure defense plant or every airline passenger who is a frequent lyer with United Airlines. It is possible to
determine how many features an automated scanning system has to distinguish on how many different ingers to tell apart some speci ic number of people. The
theory behind this technology is, of course, the basis for automated ingerprint identi ication systems. And it is important in getting at the question of ingerprint
individuality, because it represents an automated method for comparing large numbers of prints for individual characteristics.
Nature of Fingerprints
The beginning of the recognition of ingerprints as a unique personal identi ier is shrouded in the mists of history. Fingerprints are the result of a type of skin
called friction ridge skin, which is found on the ends of the ingers, in the palms, and on the soles of the feet of primates, including humans. Though palm prints
and footprints can be compared and analyzed, the most work has been done on ingerprints.
As shown in Figure 8.2, there are three basic ingerprint patterns: arches, loops, and whorls.
Figure 8.2: Three basic ingerprint patterns
Can you see the differences between the ingerprint patterns? Which patterns are on your ingers?
Adapted from andregro4ka/iStock/Thinkstock
An important development in the history of ingerprints was classi ication systems. Classi ication schemes are based on all 10 prints from an individual. The basic
pattern is determined from each print, and within the basic patterns, ingerprints have certain ridge features that they all share. Fingerprint examiners call these
features minutiae (singular: minutia), and three of them are important to ingerprint examiners when they compare prints. These are the dot, the bifurcation, and
the ridge ending (see Figure 8.3). Note that these minutiae can be present in more than one place in the print pattern and that the location varies from print to
print. The type, number, and location of minutiae within a print form the basis of its individuality.
Figure 8.3: Key minutia features
Now that you know the ingerprint patterns on your ingers, examine them again. Can you ind examples of the key
minutiae features? (It is easier if you make a ingerprint to look at).
Adapted from ponsuwan/iStock/Thinkstock
Think About It
Compare the patterns and minutiae of your ingerprints with friends or family members. Do you see the differences? Do you think ingerprints are an
accurate and reliable way to identify people?
History of Fingerprints for Identi ication
There are indications from archaeological excavations that the use of ingerprint and handprint patterns as methods of personal identi ication dates back
thousands of years (Berry & Stoney, 2001). They are thought to have been used as signatures and marks of authenticity.
The study and use of ingerprints as unique identi iers can be traced to the 17th and 18th centuries in Europe. The English plant morphologist Nehemiah Grew
(1641–1712) published very accurate drawings and descriptions of ridge patterns in a paper called “The Description and Use of the Pores in the Skin of the Hands
and Feet,” published in the Philosophical Transactions of the Royal Society of London (1684). Then Johannes Evangelista Purkinje (1787–1869), a Czech
physiologist, wrote about friction ridge patterns and described a number of ingerprint patterns in his thesis in 1823. Thomas Bewick (1753–1828) was primarily
known as a wood engraver whose engravings appeared in books. He appears to have “signed” his work with his own thumbprint, believing it to be as unique as his
signature.
British civil servants in India, beginning around 1850, were important contributors to the development of ingerprints as a means of personal identi ication. One
such person, Sir William Herschel, is often credited with being the irst European to recognize the value of ingerprints as a means of identifying individuals. Dr.
Henry Faulds, a Scottish physician, is known to have been involved in the study of ingerprints by at least 1879. Faulds noted that ingerprints could be classi ied
and that ridge detail appeared to be unique, and he mentioned the idea of apprehending criminals by locating ingerprints at scenes. He wrote to Charles Darwin
(the scientist responsible for proposing the theory of evolution) about ingerprints, who then forwarded the letter to Francis Galton. Galton, a well­known scientist
and early genetics researcher, has been said to have put the study of ingerprints on scienti ic footing. Galton became interested in the subject of ingerprints and
put much thought into iguring out how to show that ingerprints were individual. Fingerprint minutiae are sometimes called Galton features in recognition of his
contributions. Thomas Taylor, a U.S. Department of Agriculture microscopist, noted in a scienti ic journal article in 1877 that ingerprints and palm prints might be
used as identi ication features, especially in criminal matters.
To understand and appreciate how ingerprints came into widespread use, some background on a technique called anthropometry is necessary. Anthropometry
involves the measurement of the human body and its parts and can be regarded as the irst recognized biometric identi ication method. This method was created
by Alphonse Bertillon (1853–1914) and laid the foundation for the eventual acceptance of a biometric parameter as an objective basis for personal identi ication
in a law enforcement context. Bertillon came up with this concept while working with the Paris Police Prefecture, where his duties included illing out and iling
criminal information cards. The criminals were skilled at avoiding identi ication by using disguises and aliases. It occurred to Bertillon that individual physical
features could be used to uniquely identify people on criminal records, and he developed a system of measurements that included head size, inger length, and so
forth, ultimately choosing 11 different measurements. The information was recorded on ile cards, and a system was devised for organizing the iles. His superiors
doubted the system, but it soon proved its value by enabling the police to identify repeat arrestees even if they provided alias names. Bertillon eventually became
director of the identi ication bureau of the Paris Police. Police agencies in many other places began to use his system—often called Bertillonage. Its ultimate
undoing was the unequivocal proof that different individuals could have the same anthropometric measurements.
A well­known example of this chance duplication came at the US federal prison at Leaven­worth, Kansas. A new prisoner named Will West was having his
measurements taken when a staff member began to suspect that he had encountered this pro ile before. Upon investigation, he found that the same
measurements it a man named William West who was already incarcerated at the prison (and unrelated to Will West, although they looked a lot alike). However,
the two did have different ingerprints. This incident, and others like it, eventually convinced police identi ication specialists that ingerprints represented the
basis for a superior method of personal identi ication.
Around 1893 the British Home Of ice, parent agency of the London Metropolitan Police (Scotland Yard), decided to add ingerprints to the Bertillon cards for
criminals in its identi ication system. Before long, the success of ingerprints overshadowed that of Bertillonage in criminal identi ication, and anthropometry was
abandoned in 1901.
Sir Edward Henry (1850–1931) was a member of the British Indian Civil Service, beginning in about 1873. In 1891 he became inspector general of police for
Bengal province, where anthropometry was in use for criminal identi ication. He became interested in ingerprints, read Galton’s book, and corresponded with
and later visited him. Galton shared all the information he had about ingerprints with Henry, including materials he had obtained from Herschel and Faulds.
Henry is widely known for working out a ingerprint classi ication system that was adopted in British India and presented to people in the United Kingdom in
1899. He wrote a classic book entitled Classi ication and Uses of Fingerprints.
Juan Vucetich (1858–1925) was the western hemisphere’s ingerprint pioneer. An employee of the police department in La Plata, Argentina, he became convinced
of the value of ingerprints as a means of criminal identi ication and wrote a book on the subject in 1894.
By 1896 the Argentine police had abandoned Bertillonage in favor of ingerprints in criminal records. The irst recorded case in which ingerprints were used to
solve a crime took place in Argentina in 1892. A woman named Francisca Rojas alleged that her two children were murdered by a man named Velasquez.
Investigators examined her home and found a bloody thumbprint on the bedroom door. Vucetich compared the ingerprints of Rojas and Velasquez to the bloody
ingerprint and that found it belonged to Rojas, linking her to the murder of her children. Vucetich devised a classi ication system for ingerprints that was used in
Argentina and throughout South America.
In North America, ingerprints were in use by the New York City civil service (to prevent impersonations during examinations) by 1903, and ingerprints were
introduced about the same time in the New York State prison system and at Leavenworth. A number of police departments began using ingerprints as identi iers
in criminal records as well. The 1904 St. Louis World’s Fair provided the venue for a chance meeting between Inspector Edward Foster of the Royal Canadian
Mounted Police (RCMP) and Detective John Ferrier of Scotland Yard. As a result of what he learned in St. Louis, Foster convinced his superiors in the RCMP of the
utility of ingerprints. In 1910 a man called Thomas Jennings was arrested in Chicago and brought to trial for murder. The primary evidence against him was
ingerprints. The state, which wanted to ensure that the ingerprint identi ication evidence would survive the anticipated appeal to the Illinois Supreme Court,
called Edward Foster as an expert witness. The defendant was convicted, the evidence did survive, and the Jennings case is considered a landmark ingerprint case
in criminal jurisprudence.
Fingerprint Identi ication Organizations
Now that ingerprints have become a major biometric indicator and play an important role in criminal investigations, there are a couple of important
organizations that ingerprint examiners may choose to become a part of. The International Association for Identi ication (IAI) is the primary professional
organization for ingerprint examiners. It has extensive certi ication programs, and its latent print certi ication is dif icult to obtain. Many physical pattern
comparison specialists also belong to the IAI.
Another important group is the NIST OSAC Friction Ridge Subcommittee (FRS). This committee is a consensus standard–setting body for all comparisons
involving friction ridge skin ( ingerprints, footprints, palm prints). This group supplanted the Scienti ic Working Group on Friction Ridge Analysis, Study and
Technology, which was the previous standard­setting body for this specialty.
Fingerprint Classi ication and File Storage
When all ingerprint records consisted of inked impressions on a 10-print card, a classi ication system was very important. How else could the cards be iled so
that they were easily found? Classi ication was based on a 10­print card, not on a single print. You needed all 10 prints from a person to classify the prints.
In most criminal cases in which ingerprints are recovered, there is only one—or sometimes only a partial—impression of one inger. In such a case, how would
authorities locate it in their card ile? Simply put, they couldn’t, which was the problem. Sometimes there might be one or more suspects, and their ingerprints
could be pulled for comparison. But if there weren’t any suspects, there was no realistic way to search drawers that were full of iles to look for one ingerprint.
That is why the advent of the Automated Fingerprint Identi ication System (AFIS) revolutionized the use of ingerprints.
The system consists of a scanner that records images of all 10 prints and stores them on a server. It includes many workstations from which operators can enter
new ingerprints and search the system for existing ones. The way in which the system works is relatively simple. The examiner begins by scanning a ingerprint,
and computerized algorithms mark the minutiae to search for. The computer then calculates a score based on the degree of match. Most of the time, the matching
print will appear in the irst few entries, if it is in the system. The examiner must pull up the likely matches and visually compare them with the ingerprint in
question. The computer is not used for matching prints for court purposes. That is something only an examiner can do. AFIS is used to provide possible matches,
helping narrow down the list of individuals the ingerprint could belong to. An examiner will then need to compare the ingerprint and the possible matches
provided to make the inal decision on the identi ication of the ingerprint.
Think About It
Do you think that 10­print cards and/or AFIS systems are a good way to organize and store ingerprint data? What other ways can you think of that could
improve the iling system?
8.5 Collection and Preservation of Fingerprints
There are two topics that must be considered in terms of collecting and preserving ingerprints for a case. The irst is collecting or taking ingerprints from known
individuals. The second is collecting ingerprints from crime scenes and objects.
Collection and Preservation of Knowns
At one time, ingerprints were taken from known individuals by inking the ingers and impressing them onto ingerprint cards (as seen in the cover photo for this
chapter). In addition to including a labeled box for each inger, there was space on the bottom of the card to reprint the thumbs and to impress the four ingers of
each hand. These impressions served as backups if the main boxed impressions were not of high enough quality for a comparison. Fingerprints from these 10­
print cards can be scanned into AFIS systems to build the single­print databases.
Today most ingerprints are collected by Live Scan technology. The person places each inger (and thumb) onto a small scanning plate. Sometimes there is an on­
screen guide to help the person adjust the position and pressure of each inger. The device then scans the prints directly into an AFIS. These devices can be seen at
ports of entry into the United States, such as in international airports.
Fingerprints are also preserved electronically. The largest database of ingerprints is contained in the FBI’s Integrated AFIS (IAFIS) system. The system contains
over 70 million print iles from criminal histories and about 35 million other iles. People who are arrested are ingerprinted. But many other people may be
ingerprinted as well, like those who have irearms permits or security clearances or have undergone background checks for a variety of reasons.
Collection, Preservation, and Processing of Evidentiary Prints
Collecting ingerprints from scenes is similar to collecting evidence from a scene, but it is more complicated than collecting known prints. Sometimes prints at
scenes are visible, but often they are not. The ones that are not require some sort of development or processing to render them visible. The irst decision an
investigator must make is whether to use development (visualization) techniques for prints at the scene or to bring the object bearing the print back to the lab.
The larger and more unmovable the object or surface, the more likely an investigator would be to employ development techniques in the ield. After locating
and/or developing the print or prints, the crime scene processor must either collect the whole object the print resides on or collect the ingerprint alone.
Photography and sketches are used to document the location of the ingerprint or the object containing it at the scene. The print or developed print must also be
photographed. It is best if the photo can be 1:1 (life­size image). That way there is no compression of the details. If a print has required development, it may be
possible to tape­lift the print, depending on the type of development. All the usual rules about chain of custody pertain here. The item bearing the print or the
tape­lift must be carefully packaged, labeled, and sealed. Items have to be packaged so as to provide maximum protection of an undeveloped print impression.
Nothing should touch or rub the impression during storage or transport. Some type of wood or plastic trough must be used to protect the ridge impressions from
the package during transport. Developed latent prints must also be protected. Tape­lifts are placed onto backings and are thus protected.
Duties of a Latent Print Examiner
A latent print examiner explains some of the duties and procedures involved in his
work.
There are three kinds of ingerprint impressions encountered: visible, plastic, and latent.
Visible Fingerprints
Visible prints are also sometimes called patent. Visible prints are made in dirt, ink, blood, or some other medium that is visible to the eye. These would be
photographed and, if possible, the object on which they are deposited would be collected.
Plastic Fingerprints
Plastic prints are three­dimensional and are made in soft receiving materials like silly putty or tar. These are indentation prints. They are irst photographed. Then
the object bearing the print is collected, if possible. If not, this type of ingerprint impression can be cast in the same manner as footwear indentations, only the
casting materials are silicone­based and capable of capturing ine detail much better than any type of plaster.
Think About It
What do the techniques and procedures for evidentiary ingerprint collection and preservation have in common with the collection and preservation
techniques for other pattern evidence? What are the differences?
Latent Fingerprints
Latent (hidden) ingerprints cannot be clearly seen or visualized without some development or processing. There are three basic methods of processing or
developing latent ingerprints: physical, chemical, and instrumental. The most common and familiar physical method is powder dusting. Here a ingerprint
powder (usually black) is applied with a ine brush to the latent print residue. The powder particles adhere to the fatty components in the residue and make the
ridges visible. Another technique used is called magna brush. Here a small magnet is used to apply magnetic particles to the print residue. These particles adhere
to the latent residue the same way as the powder particles. Powder­dusted (including magna­powderdusted) prints can generally be lifted using transparent tape.
The tape must be placed carefully onto the dusted print to avoid any air bubbles. This can be done with a rubber roller. The tape is lifted all in one slow motion,
and the transparent tape­lift is then placed onto a contrasting background, such as a white surface. Another, more complex technique uses molybdenum disul ide
particles in a solution. This is known as small particle reagent and works on surfaces that are wet. Lifting of a print developed via small particle reagent can be
accomplished without letting the surface dry if the tape is carefully applied to the center and pressure applied in all directions outward, pushing away the liquid
droplets in the process. Latents on wet surfaces aren’t common, but the situation does arise. Think of a can of beer with a latent on it, taken from the refrigerator
and allowed to sit out for a while in a humid environment where water can condense onto the can.
The classical chemical techniques for print development were silver nitrate, iodine
fuming, ninhydrin, and superglue. Silver nitrate development works on the same
principle as the development of photographic ilm, in which silver chloride is
chemically reduced to metallic silver. Iodine fuming is based on iodine molecules going
from solid to vapor without becoming liquid (a process called sublimation). The iodine
vapor can interact with ingerprint residue and give it a temporary color. The color can
be made permanent with other chemicals. Neither silver nitrate nor iodine are used
for latent prints anymore, because the other techniques are better or equivalent. Silver
has gotten expensive, and it creates a disposal problem after use. Other techniques are
better than iodine because they have the potential for greater sensitivity.
Today ninhydrin or superglue treatment is followed by an additional treatment with
other chemicals to make the visualization more sensitive—that is, lesser amounts of
residue can be detected. Ninhydrin is a chemical that reacts with the amino acids in
ingerprint residue. Amino acids are the building blocks of proteins. Superglue can be
fumed onto ingerprint residue, where it reacts to form a semisolid, whitish deposit on
the ridge patterns. Superglue will vaporize by itself, and the process can be accelerated
with heat. The vapors, or fumes, interact with the ingerprint residue. The superglued
ingerprint is fairly permanent, but it can be powder dusted and the dusted print lifted.
This is done in the same way as lifting dusted ingerprints, as described earlier.
Superglued prints can also be further treated with other chemicals by dipping or
spraying to make the visualization more sensitive. Ninhydrin is the method of choice
for absorbent surfaces like paper or Sheetrock. Superglue will work on practically any
surface.
Franz12/iStock/Thinkstock
Fingerprints at the scene of a crime are often latent and are found after
an investigator has dusted or used another method to look for them.
The most common instrumental technique is called laser illumination. With this process, ingerprints are commonly developed with superglue, on which a
chemical called laser dye is applied. When a laser is shined on a ingerprint processed in this way, a very small amount of residue can be visualized and then
photographed. Sometimes laser illumination is used directly on ingerprint residues, but this technique is used less frequently. Laser procedures are usually
performed in the lab. Portable lasers do exist, but these techniques are very cumbersome in the ield. Laser­illuminated prints would typically be photographed
for comparison. The laser dye procedure is indicated if the ridge patterns are not clear enough for a comparison following superglue development alone.
Fingerprints in blood can be a special case. Sometimes they are plainly visible (in these cases these would be considered visible prints), but at other times they
may require special enhancement techniques. The enhancement procedures make use of chemicals that produce color in the presence of blood. They also contain
a sticky substance to make them adhere to the residue and a rapidly evaporating solvent so that bloody prints on a vertical surface don’t run when the chemical is
sprayed. These enhancement techniques have the potential of interfering with DNA pro iling of the blood because the chemicals in the enhancement mixture can
adversely affect DNA. It is important for investigators to consider the value of DNA pro iling and ingerprint identi ication to the case in these situations. A small
specimen of blood could be collected, for example, without disturbing the ridge patterns a ingerprint examiner would need.
Think About It
If you had to choose a single method for processing latent prints in the laboratory, which one would you choose and why? Is choosing a single method
appropriate?
8.6 Analysis of Fingerprints
For forensic and legal purposes, ingerprint analysis or comparisons are the heart of the matter. The comparison of a questioned print with a known, and the
ability to form an unequivocal conclusion, make ingerprints valuable as evidence.
Trained examiners complete the comparisons. The training is lengthy. It can take up to 2 years before a new examiner is allowed to operate without supervision.
There is a speci ic protocol to be completed for each comparison. The irst thing to be decided is whether the print is suitable for comparison. This decision is
based on the clarity of the ridges and the examiner’s judgment that a proper comparison can be completed. For example, the examiner must determine if there is
enough of the print present in the impression and if there are enough visible details (minutiae). The examiner must also determine if the print is easily viewed, is
not smudged, and does not have too many impressions overlaid on one another. If the print is judged to be unsuitable for comparison, the examination ends. If the
print is judged to be suitable, the questioned print must be properly oriented for comparison with a known (a whole ingerprint). To perform an accurate
examination, the print cannot be upside down or rotated 90 degrees. Next it goes through analysis, comparison, evaluation, and veri ication (ACE­V) . Analysis
consists of judging suitability, arranging correct orientation, and judging the minutiae content of the print. The comparison part is carefully iguring out if every
minutia feature in the questioned impression is also in the known—and in the same location. The evaluation step is based on the examiner’s knowledge of and
experience with print comparisons. How common or rare is this pattern? If the examiner is satis ied that there is enough detail and are no unexplained differences
between the questioned and known, an identi ication can be made. In the veri ication step, another examiner is asked to look at the prints and verify the irst
examiner’s conclusion.
As shown in Table 8.1, the main category to which the ingerprint belongs (arch, loop, or whorl) is sometimes called irst level, or level 1. The minutiae present
and their location are sometimes called second level, or level 2. There is a level 3 as well, consisting of pores and ridge features. Level 3 is not always used, because
the irst two levels are nearly always suf icient for making an identi ication or determining an exclusion.
Table 8.1: Fingerprint pattern levels
Level
Pattern category
1
Arch, loop, or whorl
2
Minutiae (such as dot, bifurcation, and ridge ending)
3
Pore and ridge features
An examiner may reach three possible conclusions following a comparison: exclusion, inconclusive, or identi ication. Exclusion means that the questioned print
does not match the known print, and therefore the person to which the known print belongs is excluded. Inconclusive means the examiner can neither make the
identi ication nor exclude the person. There isn’t enough information in the questioned print. Identi ication means that this questioned print is attributable to
the person who furnished the known.
In recent years there have been questions as to whether there is a suf icient scienti ic underpinning to ingerprint comparisons to warrant the identi ication
conclusion (National Research Council, 2009; Koehler & Saks, 2010). How do we know ingerprints are individual? The standard answer is that hundreds of
thousands of prints have been compared, and no two have been found that are alike. This standard answer is correct in a sense, but one person did not analyze all
of these pairwise comparisons. That is, the sum total of all the pairwise comparisons was done by many different people at different times. Furthermore, an
examiner doesn’t compare a questioned print with millions of knowns; the questioned print is compared with only a few. With AFIS systems, the multiple pairwise
comparison argument is much more supportable. If a questioned print is searched within IAFIS and found, that questioned print was compared with all the prints
in the database. To date, no one has found two or three matches—only one (or none, if the print isn’t in IAFIS). The fact that so many searches have been
completed lends considerable support to the individuality idea, but you can make the valid argument that a duplicate has not been found simply because it was
not in the system.
Think About It
From everything you have learned so far, do you think there are two people who have exactly the same 10 ingerprints? What about two people who have
one ingerprint identical to one of the other person’s? What about two people who have a partial of one ingerprint identical to the partial ingerprint of the
other person?
Nevertheless, a high­pro ile case from 2004 has caused some of the thinking to be reconsidered. The real question is not so much whether complete ingerprints
are duplicated to the extent that a trained examiner can’t tell them apart, but whether there is a chance to get a partial duplicate. That is, presented with an
incomplete questioned impression, could there be two prints out in the world that could be interpreted to “match”? See what you think after reading the case of
Brandon May ield v. United States.
Case Illustration: Brandon May ield v. United States
Brandon May ield was a Muslim attorney practicing in Oregon. He was a U.S.
citizen and army veteran. He converted to Islam after meeting and marrying his
Egyptian­born wife. On March 11, 2004, a series of coordinated bombings did
extensive damage to Spain’s commuter train system in Madrid, killing 191 people
and wounding around 1,800 others. The attack was perpetrated by a local terrorist
cell, inspired by but not directly connected to al Qaeda. In the subsequent
investigation, a bag containing detonating devices was recovered by the Spanish
police, and latent ingerprints were found. These were shared with other
countries’ law enforcement agencies to help with the case.
The FBI ingerprint unit ran an AFIS search and generated a number of potential
matches. May ield’s prints were among them. Possibly because he was Muslim and
had provided legal assistance to some Muslim clients, he became a principal
suspect. FBI ingerprint experts working on the case came to the conclusion that
the evidentiary latents matched May ield, and several of them—all highly
experienced and seasoned examiners—agreed on this conclusion. The FBI
conducted a detailed investigation of May ield and eventually arrested him. There
were discussions and at least one meeting between FBI examiners and Spanish
ingerprint examiners, in which the latter told the FBI that the prints did not match
May ield. However, the FBI continued the investigation until it became clear that
the FBI was incorrect on this identi ication. It was found that the prints belonged
to an Algerian national named Ouhnane Daoud.
The FBI released and apologized to May ield, and the government settled a suit he
iled against it for $2 million. There was a public discussion involving federal
overreach in the investigation, aside from the ingerprint issue. May ield sued the
government, seeking to overturn parts of the Patriot Act (Lichtblau, 2006). Some
sections of the act were initially overturned in lower courts, but federal appellate
courts reversed this action upon government appeal in 2009 (Denson, 2009).
Re lect On It
What do you think about the misidenti ication of this case? Was it bias, incorrect
examination of the ingerprints, or a combination of both that led to the wrong
arrest? What do you think could have prevented this?
Don Ryan/Associated Press
Brandon May ield at a press conference.
It has been suggested by ingerprint critics that misidenti ication occurred in this case because of examiner bias. They state that FBI experts knew all about the
case and thought it should be a match and that this knowledge ended up deeply prejudicing them. In any event, it does show that identi ication errors can happen.
You may be thinking as you read this section and this case example, why isn’t there a minimum number of points to de ine a match? It sounds easy, but it isn’t.
There was such a criterion in the United Kingdom for quite some time. But it turned out that nonmatching ingerprints could have the minimum required number
of points. It is also the case that an examiner may not always have the minimum number but is convinced the prints match. For these reasons, the IAI, the
professional organization that makes international consensus statements about these matters, has long taken the position that there should not be a speci ied
number of matching minutiae or points to declare a match. As noted, the IAI is continuing to examine its principles regarding ingerprint identi ication (Polski et
al., 2011). For a review of the ingerprint individuality subject after the NAS report, see the Eldridge article in the Web Resources section at the end of the chapter.
Another way of looking at examiner accuracy is through pro iciency tests. Examiners are subjected to these pro iciency tests for certi ication and recerti ication.
Some agencies and accredited forensic labs also participate in pro iciency testing for their examiners. At times the tests can be done for research purposes as well.
In pro iciency tests, examiners are given sets of questioned prints or partials along with known prints and told to complete pairwise comparisons and form
conclusions. The vast majority of tests and studies of this type show that the examiners get the right answers. One study involving the ingerprints of identical
twins resulted in a few misidenti ications (Grieve, 1996). Identical twin ingerprints are distinguishable, but they can be very similar.
Analysis of Other Friction Ridge Impressions
Friction ridge skin impressions, such as palm prints and footprints, are compared in the same way as ingerprints are compared. To clarify, oftentimes people refer
to “footwear impressions” as footprints, but this is incorrect. Footprints are made by bare feet. The main difference between these types of friction ridge skin
impressions and ingerprints is that iles of palm prints or footprints are not maintained, because these impressions are less frequently encountered than
ingerprints. Generally, investigators must develop one or more suspects, then arrange to collect inked palm or foot impressions as knowns for comparison. The
methods used for comparison and the criteria for conclusions are the same as for ingerprints.
Can Fingerprints be Altered?
A ingerprint expert discusses the futility of trying to erase one’s ingerprints.
Conclusion
Patterns are an important class of evidence. Identi ication patterns refer to the mental images used to classify objects in the environment. Individualization
patterns can be physical patterns or impressions. The most commonly seen impressions are footwear and tire tracks. Reconstruction patterns help investigators
form theories about events that took place in the past, based on the physical evidence record.
Pattern evidence is collected by photography, lifting, and casting, as appropriate. It is analyzed by comparing a questioned impression with a known impression or
object. A proper comparison requires that only like impressions be compared (positives, negatives, left, right, etc.). Some pattern evidence can sometimes be
individualized.
Fingerprints are an important category of evidence and have a lengthy history of use as a means of personal identi ication. Automated ingerprint identi ication
systems have enabled the storage and search of single ingerprints and have rendered 10­print cards and classi ication systems obsolete. At scenes, visible, plastic,
and latent prints can be found. Latent prints require some visualization techniques to make the ridge detail suitable for comparison. There are physical, chemical,
and instrumental methods for developing latent prints. Questioned ingerprints are compared with known prints, and examiners can often individualize the print
to a person or exclude a person as the source. Sometimes prints are not suitable for comparison, or there is insuf icient detail to reach a conclusion. There has
been discussion about the scienti ic basis for ingerprint individuality and whether individualization is justi ied in ingerprint comparison, particularly with
questioned partial prints. Palm prints and footprints are sometimes encountered at scenes, and they may be compared to knowns in the same way as ingerprints.
Take the role of an expert in footwear impressions, work through a case, and testify as an expert witness.
Key Ideas
•
•
•
•
•
•
•
•
There are patterns for identi ication, for individualization, and for reconstruction.
Important patterns for individualization include physical matches, as well as imprint and indentation markings, of which footwear and tire impressions
may be the most common.
Fingerprints are an important class of physical evidence and an example of a biometric identi ier.
AFIS systems enable rapid search and retrieval of single ingerprints.
Latent ingerprints require visualization or processing steps in order to be suitable for comparison.
There is a method for ingerprint (and other friction ridge print) comparisons called ACE­V, which describes the steps an examiner follows to compare
questioned and known prints.
Fingerprints are individual. With very rare exceptions, identi ications or exclusions can be made following a comparison by a quali ied examiner.
Footprints and palm prints are compared in the same manner as ingerprints.
Critical­Thinking Questions
1.
2.
3.
4.
5.
In a criminal aggravated assault case, the accused ripped off the victim’s dress, and in the process, a piece became completely separated and got stuck on
the back of the perpetrator’s shirt. The police later recovered the shirt, which still had the fragment of dress on it. Imagine that you are the lab examiner,
comparing the evidential fragment to the dress. This is a summer­weight, light material with a distinctive, decorative pattern on it. The fragment lines up
almost perfectly with a missing area on the victim’s dress. Color and pattern are the same. Thread count is the same. It de initely could be the missing
piece. How would you testify to this inding?
In a criminal case, a suspect is thought to have kicked in a metal door while wearing a sneaker. The police successfully use an electrostatic dust lifter to lift
a good dust print of the sneaker from the door. They also have a suspect and the sneaker they think probably made the mark. How would you, as the
examiner, make the “known” sneaker impression to compare with the dust print?
A government agency is willing to fund a study to establish that ingerprints are really individual. How would you design this study? Describe the study
design, the results that might be expected, and the conclusions that could be drawn from them.
In a homicide case, the police ind a good bloody footprint on a bathroom loor tile. They think the footprint belongs to the perpetrator. They have a
suspect in custody, but they cannot prove he was at the scene at the time of the crime. You are the examiner and are given the tile with the questioned
footprint on it. How would you tell the police to collect the known footprints from the decedent and from the suspect? Do you think the police need a
search warrant to collect the known footprint from the suspect?
You are the ingerprint expert witness in a criminal trial. An object from the crime scene had a good latent print on it, and you were able to match the
latent to the known print from one of the defendant’s ingers. You have testi ied that the latent ingerprint came from the defendant. The defense lawyer
now says to you the following: “The police had a 10­print card on ile containing the defendant’s ingerprints. At the time the police arrested the
defendant, they had very little evidence that he was actually at the scene, but they were convinced he was their guy. Suppose they took some lifting tape
and carefully lifted off one of the prints from the 10­print card, then used that tape to place the ‘latent print’ on the object from the scene that was
submitted to you for examination. Do you concede that this scenario is possible? If so, would you agree that the latent match to the defendant does not
then prove that he was actually at the scene?”
Key Terms
Click on each key term to see the de inition.
accidental
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
An individual characteristic in an item of footwear, a tire, or other object that occurs as the result of wear and exposure and that can be detected in an imprint or
indentation of the item.
Analysis, Comparison, Evaluation, and Veri ication (ACE­V)
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
The process followed by ingerprint examiners in their comparisons of known and questioned ingerprints, as well as footprints or palm prints.
biometric
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
Literally, any biological feature that might be used to distinguish people. Fingerprints are an example of a biometric identi ier.
bite mark
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
A mark made in a soft receiving surface by human teeth. Human teeth, and thus the mark patterns they make, are believed to have individual characteristics.
direct
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
A physical match of pieces of a randomly fractured solid material, such as glass or plastic, in the manner of a jigsaw it.
exclusion
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
A conclusion by an examiner that a questioned specimen cannot have originated from a known specimen with which it has been compared.
identi ication
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
In pattern evidence comparisons, this term means individualization, a conclusion that the questioned specimen originated from the known with which it was
compared.
impression
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
Any mark made by an object impressing its shape and form into or onto another object or surface. Impressions can be imprints or indentations.
imprint
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
An effectively two­dimensional impression.
inconclusive
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
In pattern evidence comparisons, this conclusion means that there is not suf icient information to draw a de inite conclusion; that is, we cannot say for sure
whether the questioned is excluded or there is an identi ication.
indentation
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
A three­dimensional impression.
indirect
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
A physical match of pieces of a nonsolid item or object that has been cut or torn, or of a solid object that fractures in such a way that the pieces cannot be directly
realigned.
latent
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
Literally, “hidden.” A latent ingerprint is one that requires processing or development in order to be visible and suitable for comparison.
minutiae
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
(singular: minutia) The individualizing characteristics of a ingerprint pattern. Primarily, examiners use dots, bifurcations, and ending ridges.
ninhydrin
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
A chemical that reacts with amino acids to form a visible, violet­colored product. It is used to visualize latent ingerprints.
patent
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
Literally, “visible” or “obvious.” A patent ingerprint is visible.
plastic
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
An indentation ingerprint that has been impressed into a soft receiving surface so as to have depth.
striation
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
A sliding tool mark, resulting from one surface sliding on another and thus creating a mark.
superglue
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
A commercial adhesive, chemically a cyanoacrylate ester, which can be used to develop latent ingerprints by fuming the glue onto the print residue.
10­print card
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
Formerly, ingerprints from individuals were collected on cards formatted to hold information about the person plus inked ingerprints from all 10 ingers. The
10­print card was the basis of classi ication systems, and the cards were kept in physical iles.
visible
(http://content.thuzelearning.com/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/Gaensslen.5453.18.1/sections/cover/books/G
Able to be seen. A visible print can be seen with no development or processing.
Web Resources
Example website for AFIS:
http://www.bio­metrica.com/SYS_B_CRIMINAL_AFIS.php (http://www.bio­metrica.com/SYS_B_CRIMINAL_AFIS.php )
OSAC FRS:
http://www.nist.gov/topics/forensic­science/friction­ridge­subcommittee (http://www.nist.gov/topics/forensic­science/friction­ridge­subcommittee )
Federal special report on the case of Brandon May ield:
http://www.justice.gov/oig/special/s0601/PDF_list.htm (http://www.justice.gov/oig/special/s0601/PDF_list.htm )
The proceedings of a major meeting on impression, pattern, and trace evidence and its utility and interpretation:
Jones, N. S. (Ed.). (2018). 2018 impression, pattern and trace evidence symposium. Research Triangle Park, NC: RTI Press.
https://doi.org/10.3768/rtipress.2018.cp.0006.1805 (https://doi.org/10.3768/rtipress.2018.cp.0006.1805 )
More discussion of bite mark comparison reliability:
https://www.washingtonpost.com/news/the­watch/wp/2016/02/01/the­latest­from­the­world­of­bite­mark­evidence/?
noredirect=on&utm_term=.035694c1ccd2 (https://www.washingtonpost.com/news/the­watch/wp/2016/02/01/the­latest­from­the­world­of­bite­mark­evidence/?
noredirect=on&utm_term=.035694c1ccd2 )
Pattern Evidence II:
Firearms, Tool Marks,
and Documents Analysis
9
Steve Helber/Associated Press
Learning Outcomes
After reading this chapter, you should be able to
• Describe irearms, projectiles, and cartridge casings and the role each plays in
investigations.
• Describe proper collection and handling of irearms evidence.
• Explain irearms analysis and conclusions formed from the evidence.
• Describe gunshot residue and how it is analyzed.
• Identify tools, their marks, and how this evidence is collected and analyzed.
• Explain how documents are collected and analyzed.
Introduction
This chapter continues the discussion of patterns for individualization. It will speci ically cover irearms and tools used in cases involving forensic analysis and
disputes that arise about the authenticity or author of a document in evidence. The major premises for these identi ications are that no two guns make identical
markings on bullets and cartridge cases and that no two people have identical handwriting.
Many of the analyses completed in these areas of forensic science depend on agreement of class characteristics, followed by individual characteristics, in that
order. In Chapter 1.4 we de ined class and individual characteristics. We talked about them again in Chapter 8.3. Let’s review these concepts brie ly in the context
of this chapter’s subjects. A class characteristic places several items in the same category because they are the same in some way. For example, if an examiner is
analyzing a document to see if a suspect may have written it, analysis could be run on the ink on the paper. The results will connect the ink to a particular
manufacturer of pens. If the suspect owned or used that type of pen, he or she could be included—but so could anyone else who used that type of pen.
In irearms analysis, class characteristics are also very important because of their ability to narrow the focus of a case. Class characteristics in irearms cases are
determined by the manufacturer. They can include the number and width of lands and grooves in the barrel of a gun, the direction of twist, and the caliber of the
gun. The irearms analyst can quickly include or exclude a particular weapon as having ired a bullet through comparison of these manufactured characteristics. A
cartridge is an un ired case containing a bullet. Once it has been ired in a weapon, it is a cartridge case, or cartridge casing. Cartridge casings can also be
examined using class characteristics to identify the caliber and features of the weapon for which they are intended. There are center­ ire and rim­ ire cartridges,
and cartridge cases from semiautomatic weapons will have extractor and/or ejector markings. (The exception to these analyses is shotgun ammunition, as will be
discussed later). With irearms identi ication, individual characteristics are speci ic to a particular weapon.
Individual characteristics are random in nature. In documents analysis, the way a person writes is the product of years of development, to the point that the writer
is unconscious of his or her handwriting. Unconscious writing has combinations of characteristics that can make it easily identi ied. In terms of individual
characteristics for irearms, the machines used to put the grooves into the barrel of a gun change over time and impart microscopic striations to the barrel. These
striations, seen within the ri ling in a barrel, transfer to the surface of the bullet and can be compared to a known bullet ired from a particular gun. The same
accidental microscopic markings can be found on many tools, such as the tip of a screwdriver. All of these microscopic imperfections can be transferred to another
surface and compared back to the tool that made them.
In summary, comparison of class characteristics allows examiners to narrow the focus to a set, or class, of items, while the individual characteristics will allow
them to tell which, if any, item in the set left the markings behind. We will irst look at the comparison and identi ication of irearms in forensic science. It should
be noted here that the markings on bullets and cartridge cases from guns are a type of tool mark. That is, tool marks represent the broader general category. But
non­ irearm­related tool mark cases are less frequent in forensic casework. (You could also think of bite marks, which we discussed in Chapter 8, as a type of tool
mark, where human teeth are the tool.) A terminology note: Comparing bullets and cartridge cases with test ires from particular weapons to ind the weapon that
ired the questioned bullet is called irearms identi ication and is not equivalent to ballistics. Ballistics is the physics of projectile light through the air from barrel
to target. Ballistics can come up in reconstructions involving ired weapons, but it is not the same thing as irearms identi ication.
There is one kind of trace evidence that we did not discuss in Chapters 6 and 7, because it is closely associated with irearms: gunshot residue. This topic will be
included here.
9.1 Firearms
Over the years, research and development in irearms has concentrated on increasing their range and accuracy. Propellants, the materials used to generate
enough force to propel the bullet, were improved for range, but one of the most fortuitous developments involved ri ling in the barrels of the irearms. The ri ling
in a barrel of a gun resembles the striping of a candy cane, a spiral of raised and lowered areas on the inner surface of the barrel of a irearm. Ri ling, shown in
Figure 9.1, imparts spin to the projectile. A projectile is de ined as something that can be propelled—in the case of irearms, a bullet. When a projectile is
spinning, it is very similar to a top. While unstable and easily knocked over when not spinning, a top is very stable when spinning and tends to remain upright.
This spin, when imparted to a ired projectile, will result in stability that increases accuracy over a longer range. Some irearms examiners have compared this to a
quarterback throwing a football. If the football spirals, it will travel a greater distance with more accuracy than one thrown end over end. Ri le and pistol barrels
are ri led. Shotgun barrels are not.
Figure 9.1: Ri ling of a gun barrel
The barrel of a irearm has spiral cuts called ri ling, which is made up of a series of lands and grooves. This allows the
bullet to travel farther and with more accuracy.
Before the inclusion of ri ling in the barrel of a irearm, a bullet comparison was accomplished by comparing the caliber of a projectile to a possible irearm
manufacturer. The use of ri ling in the barrels of irearms has not only improved accuracy and range, it has had the added bene it of imparting macroscopic and
microscopic markings onto the ired projectiles. The macroscopic markings are easily seen with the naked eye and represent the lands and grooves in the barrel of
the irearm. Lands are the raised portions of the barrel and are what remains of the original surface of the barrel before the grooves were formed. The grooves are
the lowered spaces between the lands. These are some of the class characteristics that an examiner will use to determine if a particular class of weapon is involved
in a case. The microscopic markings represent the individual characteristics the examiner will use to determine if a particular weapon in the class ired the
projectile. These are also known as striations on the bullet.
Striations found in a gun barrel result in individualized patterns that may be unique among the members of their class and can be found on the ired projectile. If
all class characteristics are the same, the analyst can compare the striations. If suf icient information matches between the evidence and a known standard
generated by the analyst, he or she can say the two items came from the same gun. There are several other conclusions that can be reached by the analyst. If class
characteristics do not match between a bullet ired from a suspect’s weapon and the evidence bullet, the analyst can exclude the item, since individual
characteristics cannot match if class characteristics do not match. If class characteristics match between the standard and evidence but there is not enough
information to form a de inite link between the evidence and standard, the analyst can call the results inconclusive. This type of analysis has been accepted in the
courts since the early 1900s (National Institute of Justice, n.d.).
The idea of this type of analysis might be hard to visualize. How did those markings get into the barrel of the gun or, in the case of cartridge cases, onto the iring
pin and breech face (the back end of the barrel of the gun, which helps contain the explosive forces released upon iring)? How are they individualized? These
things relate to the manufacture of the irearm itself.
The ri ling in the barrel of a irearm is produced by one of three main methods—the broach­cutting, button, and mandrel methods. In the broach­cutting method,
blades are used to shave metal from the inside of a metal tube, which will become the barrel of a irearm. These shaved areas become the grooves in the barrel of
the irearm. The unshaved interior surfaces of the tube that remain become the lands of the barrel. Each time the blades are used, microscopic imperfections on
the blades change with use. These microscopic imperfections leave markings that are impressed into a projectile as it travels down the barrel of the irearm.
The button method involves the use of a metal plug, formed to represent the negative of what will be the inal con iguration of the inside of the gun barrel. The
barrel is formed by pushing or pulling the button through the length of the metal tube that will become the barrel in a spiral motion, pressing the grooves into the
tube. Due to the pressures involved, the compressing surface of the button changes at the microscopic level and leaves different microscopic imperfections along
the grooves of each barrel created.
The last method of forming a barrel for a irearm uses a mandrel, or rod, that has been formed to be a negative of the gun barrel. This rod is inserted into the tube
that will be the gun barrel. Hammers compress the tube around the rod. When complete, the mandrel is twisted out of the newly formed barrel. Again, pressures
exert stress on the barrel and the rod. The rod changes with each use at the microscopic level and leaves imperfections on the inside of the gun barrel that will be
transferred to bullets that are ired through the irearm. The imperfections that each ri ling method produces are what can be used to individualize a irearm.
There is another point of terminology worth mentioning here. When a irearms, tool mark, or questioned document examiner says “identi ication,” he or she
means “individualization.”
Two old cases were exceptionally instrumental in the development of the irearms identi ication ield in the United States: The Sacco and Vanzetti case in
Massachusetts and the St. Valentine’s Day massacre in Chicago.
Case Illustration: State of Massachusetts v. Sacco and Vanzetti
On April 15, 1920, there was a daring robbery of a cash payroll in South Braintree, Massachusetts. In those days, factory employees were paid in cash. Two
men were killed as they were transporting payroll cash to the factory at the time of the robbery. Police attention focused on Nicola Sacco and Bartolomeo
Vanzetti, not only for the Braintree robbery but also for another earlier holdup. The getaway car may have been the same one in both cases. When arrested,
Sacco had a .32 Colt semiautomatic pistol. Test irings and comparisons matched that gun to a bullet taken from the body of Berardelli, one of the murdered
payroll guards. A irearms examiner from the Massachusetts State Police testi ied at the trial. In 1921 both defendants were convicted of murder and
sentenced to death. The irearms evidence was the only forensic evidence in the case, and irearms identi ication was in its infancy at the time. After
voluminous postconviction legal proceedings, both men were executed in 1927.
Sacco and Vanzetti were anarchists; they believed that the government should be overthrown by violent means, if necessary—a fact that did not help their
case. There have been several reexaminations of the bullet evidence, and it has always been veri ied that the questioned bullet from Berardelli’s body was
ired by the .32 Colt handgun. However, allegations of tampering with the bullets and the gun have arisen over the years, and the chain of custody is not
very accurate or veri iable. Many people believe that Sacco and Vanzetti were arrested, convicted, and executed mainly because they were anarchists and
that this case was in fact a miscarriage of justice. This provides a classic example of how chain of custody needs to be solid in any forensic case, especially in
a capital case, which often involves irearms.
Re lect On It
The irearms evidence was the only forensic evidence in this case, although the chain of custody cannot be veri ied. Due to this, do you think the verdict
would be the same today? Why or why not?
Case Illustration: State of Illinois v. Capone
The St. Valentine’s Day massacre occurred on February 14, 1929, at a garage at 2122 N. Clark Street in Chicago. This crime was gang related, and the well­
known gangster Al Capone was behind the murders. Five members of a rival gang were lined up against the wall of a garage and massacred using
Thompson submachine guns. The perpetrators were dressed in Chicago Police uniforms, which is how they lured the victims into the location. Police were
eventually able to solve the case and tie it to the Capone gang. Bullets and cartridge cases were collected from the scene, along with the weapons, and were
examined by Colonel Calvin Goddard. He was able to associate the machine guns with the ired evidence.
After years of tolerating violent gang activity in Chicago, the public had had enough with the Chicago mob and their violence. Gang activity declined in the
city. Goddard’s involvement in this case led to the formation of a irearms identi ication laboratory at Northwestern University, which was later transferred
to the City of Chicago as its forensic lab. Goddard is considered a founding father of forensic irearms identi ication in the United States.
Re lect On It
Thompson submachine guns can ire a number of bullets in seconds. If you were the examiner for the St. Valentine’s Day massacre case, how would you go
about analyzing all the irearms evidence?
Think About It
There was a backlog of irearms evidence in public labs in the United States as of 2014. Compared with other types of evidence, such as drugs and DNA…