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Forensic Surface Metrology: Tool Mark Evidence

NCJ Number
Date Published
March 2022

Since currently there is no universally accepted system that generates numerical data to independently corroborate visual comparisons of toolmark evidence, the reported research attempted to develop such a system for toolmark evidence, proposing a methodology that objectively evaluates the association of striated tool marks with the tools that produced them.


In this study, 58 primer shear marks on 9 mm cartridge cases, fired from four Glock model `8 pistols were collected using high-resolution white light confocal microscopy. The resulting three-dimensional surface topographies were filtered to extract all “waviness surfaces”, the essential “line” information that firearm and tool mark examiners view under a microscope. Extracted waviness profiles were processed with principal component analysis (PCA) for dimension reduction. Support vector machines were used to make the profile-gun associations, and conformal prediction theory (CPT) for establishing confidence levels. At 95 -percent confidence level, CPT coupled with PCA-SVM yielded an empirical error rate of 3.5 percent. (Publisher Abstract)

Date Published: March 10, 2022