When a gun is fired, it leaves marks on cartridge cases that are thought to be unique to the gun. In current practice, firearms examiners inspect cartridge cases for “sufficient agreement,” in which case they conclude that they come from the same gun, testifying in courts as such. A 2016 President’s Council of Advisors on Science and Technology report questioned the scientific validity of such analysis (President’s Committee of Advisors on Science and Technology, Washington, DC, Executive Office of the President). One recommendation was to convert firearms analysis to an objective method. We propose a fully automated, open‐source method for comparing breechface marks on cartridge cases using 2D optical images. We improve on existing methodology by automating the selection of marks, and removing the effects of circular symmetry. We propose an empirical computation of a “random match probability” given a known database, which can be used to quantify the weight of evidence. We demonstrate an improvement in accuracy on images from controlled test fires.
A Fully Automatic Method for Comparing Cartridge Case Images

Journal: Journal of Forensic Sciences
Published: 2017
Primary Author: Xiao Hui Tai
Secondary Authors: William F. Eddy, M. Stats
Type: Publication
Research Area: Firearms and Toolmarks
Related Resources
Advancing the Understanding of 3D Imaging for Firearms Identification
Houston Forensic Science Center, in collaboration with CSAFE, has been awarded an NIJ grant to conduct a study focused on comparability of images acquired by 3D instruments manufactured by different…
Algorithmic matching of striated tool marks
Automatic matching algorithms for assessing the similarity between striation marks have been investigated for bullet lands and some tool marks, such as screwdrivers. We are interested in the investigation of…
A reproducible pipeline for extracting representative signals from wire cuts
We propose a reproducible pipeline for extracting representative signals from 2D topographic scans of the tips of cut wires. The process fully addresses many potential problems in the quality of…
An algorithm for forensic toolmark comparisons
Forensic toolmark analysis traditionally relies on subjective human judgment, leading to inconsistencies and lack of transparency. The multitude of variables, including angles and directions of mark generation, further complicates comparisons.…