Citation

Basu N, Bolton-King RS, Morrison GS. Forensic Sci. Int. Synergy 2022; 5: e100272.

Copyright

(Copyright © 2022, Elsevier Publishing)

DOI

10.1016/j.fsisyn.2022.100272

PMID

35677322

PMCID

PMC9168521

Abstract

We describe and validate a feature-based system for calculation of likelihood ratios from 3D digital images of fired cartridge cases. The system includes a database of 3D digital images of the bases of 10 cartridges fired per firearm from approximately 300 firearms of the same class (semi-automatic pistols that fire 9 mm diameter centre-fire Luger-type ammunition, and that have hemispherical firing pins and parallel breech-face marks). The images were captured using Evofinder®, an imaging system that is commonly used by operational forensic laboratories. A key component of the research reported is the comparison of different feature-extraction methods. Feature sets compared include those previously proposed in the literature, plus Zernike-moment based features. Comparisons are also made of using feature sets extracted from the firing-pin impression, from the breech-face region, and from the whole region of interest (firing-pin impression + breech-face region + flowback if present). Likelihood ratios are calculated using a statistical modelling pipeline that is standard in forensic voice comparison. Validation is conducted and results are assessed using validation procedures and validation metrics and graphics that are standard in forensic voice comparison.

Language: en

Keywords

Calibration; Validation; Firearm; Cartridge case; Feature; Likelihood ratio