Semester

Fall

Date of Graduation

2022

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Forensic and Investigative Science

Committee Chair

Tatiana Trejos

Committee Co-Chair

Luis Arroyo

Committee Member

Luis Arroyo

Committee Member

Keith Morris

Committee Member

Monica Joshi

Abstract

During firearm-related incidents, the accurate collection and detection of gunshot residues (GSR) are crucial for reconstructing events and providing investigative leads. Regardless of the strong scientific foundations in the discipline, the standard practice for GSR can benefit from increased confidence in the results and the adoption of reference standard materials and screening tools that can lead to faster turnaround times and improved efficiency. Moreover, the implementation of comprehensive interpretation approaches requires strengthening the current body of knowledge on the transfer and persistence of inorganic and organic GSR compounds (IGSR, OGSR). As a result, the overall objective of this project was to expand the capabilities of gun-violence investigations by developing novel sampling and analytical strategies for GSR detection. We aimed to accomplish this goal through three main tasks: 1) Developing and validating analytical techniques and portable instrumentation for accurate GSR detection, 2) Developing a characterized in-house OGSR reference standard for quality control, method validation, and building knowledge on transfer and persistence, and 3) Performing systematic studies for the transfer and persistence of IGSR and OGSR on alternative matrices.

This study investigated several spectrochemical methods that allowed the interrogation and detection of IGSR and OGSR. Development and validation studies were performed for emerging analytical techniques, including LIBS and LA-ICP/MS, and methods that use instrumentation widely available at crime laboratories, such as GC-MS, LC-MS/MS, and SEM-EDS. Over 500 specimens collected from known shooters and non-shooters were analyzed to assess the methods’ feasibility for trace GSR detection. Furthermore, a novel portable LIBS instrument was optimized and demonstrated reliable use for in-field screening of authentic gunshot residue specimens. The portable LIBS showed improved detection capabilities over benchtop systems due to enhanced CMOS detector technologies, an ablation cell custom-made for GSR examinations, microscopic visualization of particle morphology, and unique capabilities for single-particle analysis.

Second, this study characterized an OGSR standard solution containing eight common analytes found in propellant formulations for its combined use with pGSR standards. A ruggedness test optimized storage conditions and sample preparation methods necessary for prolonged use of the standard, demonstrating stability for over 14 weeks. These one-of-a-kind pGSR/OGSR standards with known particle counts, chemical composition, and analyte concentrations, provided “ground truth” information in controlled transfer and persistence studies.

Finally, this research conducted an extensive transfer and persistence study on IGSR and OGSR, consisting of over 800 samples collected from multiple matrices (e.g., authentic shooters, fabric samples, and synthetic skin membranes) and exposed to diverse activities and conditions. The utility of novel synthetic skin membranes (StratM®) models for understanding the post-deposition behavior of gunshot residues is demonstrated for the first time.

The combined advantage of characterized GSR standards, synthetic skin substitutes, fast screening tools, and additional confirmatory methods, developed in this research, is anticipated to transform the current approaches used for analyzing and interpreting gunshot residues. Furthermore, implementing accurate portable LIBS instrumentation will open opportunities for in-field and triage screening testing otherwise unavailable to law enforcement.

Embargo Reason

Publication Pending

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