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Establishing Scientific Criteria for 3-D Analysis of Cartridges

NCJ Number
Date Published
November 2017
2 pages

This report describes the features and effectiveness of the "TopMatch" system, which was developed in 2013 by Ryan Lilien at Cadre Research Labs and which he describes as a "3D surface topography imaging and analysis system for firearm forensics based on the GelSight imaging technology and custom feature-based image comparison algorithms."


"GelSight," which was developed at the Massachusetts Institute of Technology, is a novel technology for measuring high-resolution surface topography. The U.S. Justice Department's National Institute of Justice (NIJ) funded research intended to establish TopMatch's base credibility by establishing the best scanning practices and demonstrating that the method meets the quality-control criteria of other forensic instruments. The report on this research indicates that the testing established best practices (cleaning, lighting, and camera settings); demonstrated excellent repeatability and precision; eliminated the concern of persistence contamination; and showed that both novice and experienced operators can collect high-quality scans. NIJ then funded Lilien's work in a related research project that scanned and compared firing-pin impressions (FPIs) on bullet casings. This study created a scanning protocol and deployed the system to crime labs for verification of its abilities. Lilien also developed software for "virtual microscopy," which enables investigators to examine virtual casings instead of the physical casings. This facilitates inter-lab collaboration and consultation without transferring the evidence from lab to lab.

Date Published: November 1, 2017