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Term of the Month

Defining Criminal Justice Research

Welcome to NIJ’s Term of the Month. Each month we are featuring a term from our scientific research portfolios informing significant American justice system issues and solutions. 

September 2022 - Virtual Comparison Microscopy

Virtual comparison microscopy image scan
Cadre Research LLC (see reuse policy).

Virtual comparison microscopy is the use of high-resolution 3D surface scanning and measurement in the field of firearm and tool mark analysis. The accurate surface imaging of bullets and shell casings with 3D visualization tools and advanced algorithms allow forensic examiners to view, annotate, conduct blind verification, and develop a statistical basis for identifying and matching ballistics evidence.

With a virtual comparison microscopy system, the bullets and casings are scanned, creating a detailed topographical map that can be shared between crime labs. The electronic file allows for the verification of findings by a second examiner. The traditional 2D comparison method requires the actual evidence — spent bullets or shell casings — to be examined directly.

Because virtual comparison microscopy files can be easily shared, they allow for better training, error-rate studies, and proficiency testing in crime labs. Although researchers expect human examiners to conduct ballistics testing for the foreseeable future, as the database of bullets, casings, and guns grows, sophisticated algorithms and machine learning could allow computers to play a significant role.

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Date Created: January 28, 2021