Success Story: Advancing 3D Virtual Microscopy for Firearm Forensics

Success Story: Advancing 3D Virtual Microscopy for Firearm Forensics

National Institute of Justice and Cadre Forensics


March 2019


Examining bullets and cartridge cases from crime scenes can help link crimes, moving investigators one step closer to identifying a suspect. Firearm forensic analysis can also link recovered evidence to a seized firearm, based on the impression pattern that the gun leaves on the cartridge case or bullet during firing. The predominant method used to compare firearm evidence is the century-old technique of comparison microscopy (essentially a split-screen optical microscope) to determine whether an evidence cartridge matches a test-fired cartridge. This method is highly dependent on variable lighting conditions and examiner subjectivity and requires that the two pieces of evidence be in the same place at the same time. In recent years, forensic laboratories have become interested in applying more advanced imaging techniques. These permit the digital capture of an accurate 3D representation of the topography of the surface being examined. This yields more reliable, reproducible images for examiners1 and points the way toward establishing an objective, quantifiable foundation for forensic firearm analysis, as recommended by the National Research Council (NRC). Cadre Forensics, led by Dr. Ryan Lilien, with support from Todd Weller, Pierre Duez, and Dr. Marcus Brubaker, developed the TopMatch-3D system for imaging of firearms evidence. Cadre based their hardware on a patented imaging technology that employs a thin elastomeric gel to accurately measure microscopic surface features. Dr. Lilien and the team also developed specialized image-matching algorithms to automatically detect and compare the 3D impression features observed on a surface with one or many other possible matches. When used for virtual comparison microscopy (VCM), the system can allow firearm examiners to more accurately and efficiently reach conclusions without having to wait for the physical exchange of evidence. Further in-lab validation studies are being conducted to quantify the performance of the system under casework conditions.

“High-resolution 3D surface topographies coupled with advanced software analysis are providing firearm examiners unprecedented new tools for microsurface examination.”

- Ryan Lilien, Ph.D., M.D. | Chief Scientific Officer, Cadre Forensics


Funding for this Forensic Technology Center of Excellence success story was provided by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice.

The opinions, findings, and conclusions or recommendations expressed in this success story are those of the author(s) and do not necessarily reflect those of the U.S. Department of Justice.

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