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Forensic Surface Metrology: Tool Mark Evidence

NCJ Number
C. Gambino; et al
Date Published

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)