Convergence-improved congruent matching cells (CMC) method for firing pin impression comparison

Area of Science:

• Forensic Science
• Ballistics
• Pattern Evidence Analysis

Background:

• Firing pin impressions are crucial for firearm identification but are challenging to compare automatically due to their concave and textured nature.
• Existing automated comparison methods struggle with the complex topography of firing pin marks.
• The congruent matching cells (CMC) method, initially for breech face comparison, offers a foundation for impression analysis.

Purpose of the Study:

• To develop advanced algorithms for firing pin impression comparison using a convergence feature.
• To improve the accuracy and reliability of automated firearm identification.
• To enhance the quantification of similarity between impression pairs.

Main Methods:

• Developed a cell-division-matching method incorporating a convergence feature for firing pin impressions.
• Employed an areal Gaussian filter for high-frequency micro-feature extraction.
• Utilized least-squares matching for precise cross-correlation and convergence of registration positions.
• Applied a density-based clustering algorithm to identify dense cell pairs and remove outliers.

Main Results:

• Achieved significant improvements in the reliability and accuracy of counting congruent matching cell pairs (CMCs).
• The developed algorithms demonstrated effective convergence of registration positions for same-source samples.
• Experiments with 40 firing pin impression samples resulted in zero false identifications or exclusions.

Conclusions:

• The convergence-improved algorithms enhance the accuracy of firing pin impression comparison.
• The method provides a reliable quantification of pairwise impression similarity for forensic applications.
• This approach offers a robust solution for automated firearm identification, reducing potential errors.