This report presents the background, features, and benefits of the TopMatch-3D system for imaging firearm bullets and cartridge cases for matching to the guns that fired them, based on the distinctive impression pattern that the gun leaves on the cartridge cases or bullet during the gun’s firing.
The predominant method for comparing firearm evidence is the century-old technique of comparison microscopy, which is a split-screen optical microscope. This method heavily depends on variable lighting conditions and examiner subjectivity. It 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 produces more reliable, reproducible images for examiners and facilitates an objective, quantifiable foundation for forensic firearm analysis, as recommended by the National Research Council (NRC). Unlike many other 3D imaging systems, TopMatch-3D was designed specifically for firearm forensics; both hardware and software were developed specifically for forensic examiners. Under grant support from the National Institute of Justice (NIJ), a team from Cadre Forensics developed TopMatch-3D, which is based on a patented imaging technology that uses a thin elastomeric gel to obtain accurate measurement of microscopic surface features. The team also developed specialized image-matching algorithms in automatically detecting and comparing the 3D impression features observed on a surface with one or many other possible matches. When used for virtual comparison microscopy (VCM), the system enables firearm examiners to reach conclusions efficiently and accurately, without having to wait for the physical exchange of evidence. Additional in-lab validation studies are being conducted to quantify the performance of the system under casework conditions.
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