2022
Ryan Lilien
Atlanta, GA
Objectives:
This presentation will share the results of recent work measuring and analyzing firing pin impressions in 3D Virtual Comparison Microscopy. The talk will cover challenges of measuring firing pin impressions, new ways of visualizing their surfaces, developments in firing pin impression specific comparison algorithms, and results on comparing these toolmarks.
Synopsis:
3D Virtual Comparison Microscopy (VCM) is a powerful tool for microscopic examination which presents an examiner with a highly detailed visualization of a toolmark surface. VCM provides a number of advantages over traditional light comparison microscopy in terms of access, documentation, visualization, and quality. Firing Pin Impression (FPI) toolmarks are a valuable part of the identification process and are likely to benefit from 3D VCM. The firing pin itself is a surface independent from the breech face and firing pin aperture. As a result, agreement seen in FPI toolmarks provides independent support to the similarity observed on the breech-face impression or the aperture shear. Analysis of firing pin impression surfaces can therefore be a critical component in cartridge case comparison algorithms. We have developed a FPI comparison method based on the algorithms we use with other impressed toolmarks. Preliminary results of the algorithm on 3D data indicate that FPIs can be useful when quantifying test fire to test fire similarity for the purposes of source identification. In this presentation we will present our work scanning and analyzing FPIs. We will demonstrate FPI scan acquisition, basic visualization, enhanced surface visualization, and the assessment of similarity via FPI specific comparison algorithms.
Additional Contributors:
Chad Chapnick, BS. (Cadre Research)
Pierre Duez, MSC, MASc (Cadre Research)
Eric Meschke, MS. (Cadre Research)
Todd Weller, MS. (Weller Forensics)
Zachary Carr, MPA. (Johnson County Sheriff’s Office)