Semester

Summer

Date of Graduation

2021

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Forensic and Investigative Science

Committee Chair

Tatiana Trejos

Committee Member

Keith Morris

Committee Member

Luis Arroyo

Committee Member

Stacey Culp

Abstract

Gunshot residue (GSR) can provide essential clues in gun-related investigations. The standard practice for GSR analysis uses SEM-EDS, with the capability for single particle elemental and morphological analysis. However, the method is time-consuming and based on categorical classification models without considering case circumstances. Therefore, complementary and more encompassing methods are needed to improve evidence interpretation of modern ammunition. This research aims to fill these demands by developing standard materials and alternative methods to characterize and interpret IGSR.

This study developed primer GSR (pGSR) standards from sixty discharged primers that were fully characterized by three techniques. The number of GSR particles, their composition, and elemental concentrations demonstrated stability for over a year, presenting an attractive resource to be used as ground truth for future studies. The standards showed some elemental profiles not yet reported in the literature, providing new relevant information.

Also, an extensive survey of low and high-risk background populations and various samples from control-shooters was obtained from the hands of 975 individuals. Authentic samples were analyzed by SEM-EDS and by a fast screening test (LIBS). Machine learning methods were applied for predictive classification with accuracies better than 90%. Also, a probabilistic assessment of the evidential value of GSR was evaluated.

This research provides the forensic science community with updated information about IGSR and a comprehensive assessment of current and novel analytical and interpretation methods. Data generated is anticipated to provide the community with a leap in knowledge and tools for more definitive conclusions.

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