Is a Match Really a Match? A Primer on the Procedures and Validity of Firearm and Toolmark Identification

• NCJ Number: 228200
• Author(s): Stephen G. Bunch; Erich D. Smith; Brandon N. Giroux; Douglas P. Murphy
• Date Published: July 2009
• Length: 9 pages
• Sale Source: US Dept of Justice Federal Bureau of Investigation
• Publication Format: Document (Online)
• Publication Type: Report (Technical)
• Language: English
• Country: United States of America
• Note: From Forensic Science Communications, V 11, N 3, July 2009; downloaded September 1, 2009.

Annotation

In addition to reviewing the standard procedure used by the FBI Laboratory to examine and identify firearms and toolmarks, this paper discusses the scientific foundation for firearm and toolmark identification, the identification criterion for a "match," and future research needs in this science.

Abstract

The paper first describes what examiners do in a firearm examination, with attention to the general examination procedure for bullets. The examination process typically begins when an examiner receives a suspect firearm, along with bullets and spent cartridge cases recovered from a crime scene. The gun is test-fired in order to recover bullets and cartridge cases that serve as controls or "comparison samples." These test-fired specimens will be compared at multiple levels with the specimens submitted from the crime scene. The description of the tasks in a firearm examination is followed by a discussion of typical examination conclusions and criteria in a firearm-toolmark comparison. In the comparison, an examiner reaches one of three conclusions: "elimination" (a discrepancy is found in the class characteristics exhibited by two compared firearm-toolmark items); "identification" (when the distinctive features of compared firearm-toolmark items are in "sufficient agreement"); and "inconclusive" (when there is agreement in the class characteristics of compared items, but insufficient agreement in the fine microscopic marks). Following the discussion of examination conclusions and criteria, the scientific foundation of firearm and toolmark identification is reviewed. The discussion includes a description of what constitutes reliable testing, i.e., strict anonymity, blind tests, clear answer sheets for test results, and the use of only qualified examiners. The paper concludes with the identification of research needs for the discipline. Additional research could assist in better addressing potential error, identify manufacturing methods that are suspect for comparison purposes, and further develop machine systems and perhaps probabilistic models. 15 references