Firearm and Toolmark Identification

The Scientific Reliability of the Forensic Science Discipline

Ronald Nichols

• Publisher: Academic Press
• Year: 2018
• ISBN:
  9780128134627
• Topic: Law
• Subtopic: Forensic Science
• Index: Law

Firearm and Tool Mark Identification: The Scientific Reliability of the Forensic Science Discipline examines the scientific reliability of the firearm and tool mark identification discipline (FATM-ID). It answers two primary questions that are necessary to assess the reliability of FATM-ID, including 1) Do different tools produce different tool marks? and 2) Can a trained examiner reliably distinguish among them? Other books published on the topic have assumed these true and have simply discussed what is involved in the discipline. This book brings together the most recent studies, serving as a well-referenced, single resource that shows that FATM-ID is scientifically reliable.

Intended primarily for firearm and tool mark examiners, this valuable resource serves as a primary requirement for the training of firearm and tool mark examiners. Finally, it will be a valuable resource for attorneys who are seeking to better understand the scientific reliability of FATM-ID. Written by a foremost expert in FATM-ID, the book provides a complete and scientific examination for anyone involved in firearm and tool mark identification.

• Provides a single resource that examines the scientific reliability of firearm and tool mark identification
• Covers the role of bias in the examination process and how it can impact the reliability of the final outcome
• Written by an expert in the field with over 25 years of firearm and tool mark experience

1

Introduction

Abstract

The desire and need for a determination of whether a particular tool was responsible for making a toolmark has existed since the late 19th century. Ideally, this would have resulted in a process in which there was an independent determination that tool-working surfaces were indeed unique and then a determination whether or not a trained examiner could discern the difference. However, due to the period in which the questions were first being asked and the lack of sophisticated technology, these two concerns could not be assessed independent of one another. It was not until recently that technology has developed to the point where these two concerns can be assessed independent of one another. Highlights of this chapter include definitions and an overview of the early historical development of firearm and toolmark identification. A discussion of the AFTE Theory of Identification is presented including a discussion of misconceptions with respect to the theory. Finally, it helps set the framework for the rest of the book, which is to assess the scientific foundations of the discipline of firearm and toolmark identification.

Keywords

Definitions; History; Introduction; Theory

Chapter Outline

• Definition and scope
• Common source determinations
• Early historical overview
• The modern era and the AFTE theory of identification
• References

Definition and scope

As a tool comes into contact with a softer material, the surface of the tool that is in contact with that material will generally mark it in some fashion. For example, when a butter knife is dragged along the surface of butter, one may observe a series of lines across the top of the butter. In this case, the mark in the butter is a toolmark and the knife is the tool that made the mark. When a bullet is fired down a barrel, the inner surface of the barrel will mark the bullet because the metal on the surface of the bullet is softer than the metal used to make the barrel, which, in this case, is the tool. When a hammer face strikes wood when a nail is missed, the hammer face makes an imprint into the wood surface, marring the wood surface. When a firing pin strikes a cartridge to fire it, the surface of the firing pin will make an imprint on the primer area of the cartridge, producing a negative image of the firing pin surface onto the area, which was struck. In each of these instances, there is a tool, which made a mark on a softer material, generally referred to as a toolmark.

In general, toolmark identification is a forensic science discipline that is primarily concerned with the determination of whether or not two or more toolmarks were created by a submitted tool. It could be that these are toolmarks left on evidence from two different crimes scenes. Or, it could be that test marks were produced by a submitted tool and compared with the toolmarks left on recovered evidence from one or more crime scenes. Either way, investigators are wanting to know if the same or submitted tool could have been used in the commission of the investigated crime or crimes. The reason is that such information would hypothetically assist them in the continued investigation of the crimes they are investigating. A forensic toolmark examiner would then evaluate the toolmarks, perform a comparison of the microscopic markings, and generally render an opinion with respect to the potential that the toolmarks were produced by the same tool or the submitted tool.

In the strictest sense of the definition, firearms consist of a series of tools that interact with bullets and cartridge cases as those tools come into contact with the ammunition components. Examples of such tools within firearms include barrels, firing pins, chambers, breechfaces, extractors, and ejectors. However, since firearms are the most common type of tool encountered in criminal cases and often the only tools examined by many forensic science laboratories, the discipline is commonly referred to as firearm and toolmark identification. It is important to keep this in mind because there is often a distinction drawn between comparisons between fired ammunition components and toolmarks created by other types of tools. While it is understandable to an extent, the separation of the two is inherently incorrect because the various parts that come into contact with bullets and cartridge cases are machined much in the same way as other tools. There are some added challenges that are introduced in the examination of marks produced by other tools, but these challenges have to do with the greater variety of materials with which other tools can interact and the manner in which they can interact with those materials. The scope of those possibilities is much more limited with firearms. But, the core principles involved in the discipline, which allow for the determination of whether or not toolmarks were created by the same tool or a submitted tool, are the same regardless of whether the tool is a firearm, a knife, a screwdriver, a pry bar, slip joint pliers, or a pipe wrench. Each of these tools is machined and the machining process leaves microscopic marks on the surface of the tool. As the tool comes into contact with the softer material, these marks are generally transferred to the softer surface in one form or another. Therefore, the core principle relates to the manufacturing process used to machine the tool surface rather than the specific tool making the tool mark.

In addition to that primary concern of whether or not two toolmarks were created by the same tool, firearm and toolmark examiners may also perform examinations of firearms to determine functionality, conversion, and restoration of obliterated serial numbers or other manufacturer-related markings. They may also be asked to provide potential manufacturer information of firearms that may have fired ammunition components based on firearm produced markings. Requests for examination may also include providing investigators with potential manufacturer information of ammunition and fired ammunition components based on bullet and/or cartridge case design. Finally, they may be asked to bring their expertise to bear in various shooting reconstruction issues such as range determination and trajectories. Therefore, the scope of an examiner’s responsibilities can and often does extend beyond determining whether or not two or more toolmarks were created by the same tool. However, it is that determination that is the most common request and will form the basis for the discussion to take place in this text.

As a specific discipline in forensic science, discussions on firearm and toolmark identification can be found in books that present an overview of forensic science as a whole. As such, it is given a more cursory treatment providing little more than an overview of what is involved in the discipline. While useful for a basic understanding of what may be involved in the various forensic science disciplines, these books generally don’t have the needed information for a deeper understanding of critical concerns of each of the forensic science disciplines in particular.

In addition to these books providing an overview of forensic science as a whole, there have been books published that deal solely with firearm and toolmark identification. Several of these were published in the mid-1930s and were authored by those who have been considered among the early pioneers for firearm and toolmark identification to include Major Julian Hatcher (Hatcher, 1935), Major Gerald Burrard (Burrard, 1934), along with Jack and Charles Gunther (Gunther and Gunther, 1935). Each of these authors discussed the various elements that would be involved with respect to firearm examination and identification to include manufacture and design of firearms and ammunition, ballistic issues, laboratory examinations of fired ammunition components and firearms, and potential reconstruction issues. They also ventured into other discussions as well. For example, two-thirds of the book published by Gunther and Gunther consisted of detailing the Sacco-Vanzetti case and court decisions regarding the admission of firearm-related evidence in the courts. However, when it came to discussing the concept that fired bullets or cartridge cases could be compared with one another for purposes of determining whether or not they were fired in the same firearm, these authors tended to come from the position that the foundation for this had already been established and that it could be reliably performed. They did identify potential obstacles to common source determinations, but each appeared content that it was valid to do so. Therefore, these seminal texts did not focus so much on the validity as much as practical application.

Books published since then follow a similar format, discussing a variety of topics relevant to overall knowledge in the discipline while coming from the perspective that the foundation for common source determinations with respect to toolmarks had been laid, and that it was a reliable practice. These include books authored by Hatcher, Jury, and Weller (Hatcher et al., 1957), John Davis (Davis, 1958), and Joseph Howard Mathews (Mathews, 1962). Hatcher, Jury, and Weller provided a significant amount of background knowledge for firearm examiners, general practice, and case histories. Davis dedicated a portion of his book introducing the striagraph, a tool that could produce a line graph of the topography of the toolmarks present around the circumference of a bullet. He believed that this would have value in helping to demonstrate the similarity of topographies of bullets fired from the same firearm. The first volume of Mathews was followed by additional volumes, which provided the reader with a wealth of information regarding data about a large number of firearms, including extensive photographs, the single most comprehensive collection of such data ever published.

One of the more recent publications was written by Brian Heard (Heard, 1997). Similar to others, he discussed the history of firearms and ammunition, ballistics, laboratory techniques, reconstruction-related issues, gunshot residues, serial number restorations, and qualifying an expert witness. In doing so, he provided a more current picture of the status of firearm and toolmark identification in forensic science laboratories. However, like the earlier authors, he came from the position that there was sufficient foundation for common source determinations and that they were reliable.

While each is valuable in its own accord, these books generally accepted a foundational tenet that bullets and cartridge cases could be compared and common source determinations could be made. Ironically, almost three-quarters of a century later, this tenet has come under attack in the literature and court proceedings, contesting the ability of a trained firearm and toolmark examiner to make reliable common source determinations. Further, there is a suggestion that what studies have been performed are less than ideal because of the individuals performing the studies. In 2009, Michael Saks and David Faigman leveled this accusation, “Most of the forensic identification sciences [which include firearm and toolmark identification], however, missed the school bus. They never joined the university system…They became an instrument of law enforcement, largely controlled by police technicians and their supervisors” (Saks and Faigman, 2008). Basically, they are suggesting that there is no sufficient foundation for examiners to make common source determinations of firearm and toolmark evidence. Furthermore, the implication is that what has been developed was done so in an environment geared toward affirming and supporting the beliefs of investigators and detectives with respect to evidence rather than being developed independent of law enforcement and then applied to law enforcement, such as was the case with DNA.

Focusing on the second of the two issues first, apart from law enforcement, there really was not a need for anyone to determine whether or not two toolmarks were made from the same tool. Therefore, comparing it to DNA, which was used to study human genetics, is not a particularly relevant argument. Throughout history, inventions and ingenuity developed out of a need, whether perceived or real. In the case of law enforcement, there was a need and desire to know if bullets could be identified to the gun from which they were fired. Therefore, they sought answers to these questions and went to the individuals that they thought would best provide them with answers, namely, individuals renowned for their expertise with firearms. Looking back, it is quite possible that they could have sought out metallurgists and others having knowledge of manufacturing processes. But, how would they know to do that? They weren’t even sure that it could be done, let alone have a better refined idea of why it could be done. So, they asked the experts in firearms and those individuals were not necessarily found in the university system. However, as will be seen, those individuals did know the right questions to be asked and reached out to the individuals that could help answer those questions.

When considering the supposed lack of sufficient foundation for examiners to make common source determinations, one of the challenges is that so much of what has been written is spread over many sources. In addition, some basic foundational elements of the discipline are found in other sciences and specialized areas such as metallurgy and metal cutting theory and practice. Therefore, an examiner has to have access to a rather extensive body of literature and knowledge to include: metal cutting and forming processes, which help an examiner understand why different tools produce different tool marks; studies that actually demonstrate that different tools will produce different tool marks; studies that help demonstrate that current techniques are reliable for firearm and toolmark identification; and a healthy knowledge of statistics and how they can be applied to the process. In addition, the examiner should be aware of the role of bias in the examination process and how it can impact the reliability of the final outcome. In short, examiners have been called upon to defend what they have concluded with respect to common source determinations regularly in evidentiary hearings and court proceedings and while the foundational blocks upon which they can draw are available, those blocks are widely scattered. The purpose of this book is to serve as a comprehensive resource that gathers these blocks together, using them in a fully developed discussion and argument for the reliability of common source determinations in firearm and toolmark identification based on studies and research conducted according to the precepts of the scientific method.

Common source determinations

In its simplest form, a common source determination is an expert opinion that two items share a common source or that an item originated from a specific source. When one considers the bulk of the work being performed in modern forensic laboratories, whether it is DNA, fingerprints, hairs, fibers, paint, glass, bullets, cartridge cases, or toolmarks, the questions asked most often by investigators is, “Did this item come from this source?,” or “Did these two items share the same source?” Depending on the type of evidence, there are varying levels of certainty that these conclusions may have. For example, DNA interpretations generally include a likelihood for a random match in the billions, if not higher. On the other end of the scale would be some of the trace d...