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Special Programs Office (SPO)

Forensic Science Program

Firearms and Toolmarks

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A man with green gloves looks at an item under a microscope

NIST researcher Alan Zheng uses a 3D disc scanning confocal microscope to examine a chisel toolmark.

Credit: ©Robert Rathe

Goal: To build a scientific infrastructure for objective forensic firearm and toolmark analysis with a rigorous evaluation of uncertainty to quantify the strength of the evidence for expert testimony in court proceedings.

What is Firearm and Toolmark Analysis? 

When a firearm is fired it leaves marks on the bullet and cartridge case. Forensic firearm and toolmark examiners compare these marks to evaluate whether a bullet or cartridge case recovered at a crime scene was fired by a particular firearm. A similar comparison is performed for marks left by other tools, such as screwdrivers, pry bars, and bolt cutters. 

Why is NIST involved in Firearms and Toolmarks? 

  • The comparison of toolmarks is currently a subjective process that relies on the skill and expertise of the examiner. NIST is working with the forensic community to augment an examiner’s testimony with objective measures for toolmark similarity and the strength of the evidence. 

  • Firearm and toolmark analysis are transitioning from the use of comparison microscopes to the acquisition and comparison of three dimensional (3D) toolmark topography images. This new technology requires standards and procedures to ensure measurement data interoperability and traceability.  

What is NIST doing? 

  • Developing standards, reference artifacts, and procedures for measurement quality assurance and interoperability 

  • Building research and reference databases of toolmarks for method development and statistical evaluation of the strength of the evidence 

  • Developing objective metrics and algorithms for evaluating the similarity of toolmarks 

  • Developing statistical models and procedures to quantify the strength of the evidence. 

Forensic Marks on a Cartridge Case
Forensic Marks on a Cartridge Case
When a bullet is fired from a semiautomatic handgun, the gun leaves distinctive markings on the cartridge case. These markings can be used to match the case to the gun from which it was fired. When the trigger is pulled, the firing pin springs forward and makes contact with the primer, igniting the gunpowder and propelling the bullet through the barrel. This contact leaves a small hemispherical mark near the center of the case. As the expanding gas propels the bullet out of the barrel, the case is pushed backward into the breech face. This creates an impression of the breech face on the rear of the case. This backward force also pushes the slide backwards. As this happens, the extractor pulls on the case, leaving a grip impression on the side. As the slide nears the end of its movement, the case makes contact with the ejector, causing the case to flip up and out of the slide. This leaves a small mark on the bottom left of the case. Credit: Sean Kelley/NIST

Associated Links

News

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Two New Forensic Firearm Examination Standards Added to the OSAC Registry of Approved Standards

Registry notches its 100th standard, marking a milestone for the forensic science organization.

See More News and Updates

Forensic Science and Firearms and toolmarks

Contacts

Forensic Science Research Firearms and Toolmarks Focus Area Lead

Subject matter expert

Measurement quality assurance

Research and reference databases

Algorithms and objective comparison

Strength of the evidence

Statistical support

Created September 21, 2022, Updated November 16, 2022