Firearm Identification in the Forensic Science Laboratory
Robert M. Thompson
Program Manager for Forensic Data Systems
Office of Law Enforcement Standards
National Institute of Standards and Technology
See also the instructional videos on "Firearms and Tool Mark Evidence"
Introduction
FOR A PROSECUTOR to be successful, he or she must be cognizant of the expectations of today's jury. Thanks to the modern electronic media, use of the forensic sciences has caught the imagination of the public, and the potential jury pool has demonstrated that it has certain expectations when a case is brought before it. No matter how fantastic or erroneous these expectations are, practitioners in law enforcement and experts in the forensic sciences have to deal with them in a forthright manner. The best strategy is for the prosecutor to be well acquainted with the capabilities and limits of the forensic science disciplines that may be the linchpin in the investigation and, more importantly, in the prosecution of a defendant at trial.
This monograph serves to introduce the prosecutor to the principal elements of one of the forensic specialties, the science of “firearm and toolmark identification.” Many of the words and terms printed in bold in the text are defined in the glossary. The monograph provides an introductory discussion of the specialty of toolmark identification when the tool involved is a firearm. The tool surfaces represented here involve one or more of the following: the interior of the barrel, the chamber, parts of the action, and ammunition magazine components. These surfaces of the firearm can produce toolmarks on fired and unfired ammunition components.The forensic scientist views a “tool” as the harder of two objects where the surface of the harder “tool” produces toolmarks on a softer material. For example, the tool surface of the hard barrel interior leaves toolmarks on the softer metal of the fired bullet. Another example is when a cartridge is fired in a firearm. The softer metal used in the cartridge case construction may show toolmarks caused by the interior chamber and action surfaces coming in contact with the cartridge case. The action is the firearm’s loading and firing mechanism.
For there to be a potential for toolmark identification, the tool working surface (1) must have individuality, and (2) the toolmarks must be reproducible for comparisons. If it is determined that the individual character of the tool working surface is reproduced in the toolmarks from repetitive markings, an examiner may be able to make an identification in later comparisons.
Read the report:
About the Author
Robert M. Thompson is the program manager for Forensic Data Systems in the Office of Law Enforcement Standards at the National Institute of Standards and Technology (NIST). Prior to working at NIST, Mr. Thompson was a senior firearm and toolmark examiner for the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) Forensic Science Laboratory in Ammendale, Maryland. Mr. Thompson was an ATF examiner for 14 years, also working in the San Francisco, California ATF Forensic Laboratory. He worked as a forensic scientist for 15 years prior to joining the ATF.