Author ORCID Identifier

https://orcid.org/0000-0002-3559-3278

Semester

Summer

Date of Graduation

2025

Document Type

Dissertation (Campus Access)

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Forensic and Investigative Science

Committee Chair

Luis Arroyo

Committee Member

Tatiana Trejos

Committee Member

Keith Morris

Committee Member

Alvaro Colina

Abstract

Understanding the collection, preservation, and analysis of gunshot residue (GSR) is crucial for making informed decisions when interpreting evidence. As gun violence continues to persist across the United States, gunshot residue evidence plays a key role in providing investigative leads and reconstruction of events in criminal investigations. Current GSR standards have a strong scientific foundation in elemental detection and classification of gunshot residues from the primer (pGSR) of ammunition. However, key information is also held in the organic (OGSR) components that are released during the discharge of a firearm. Furthermore, the GSR discipline can benefit from knowledge of collection, preservation, transfer, and persistence to provide best practices for comprehensive GSR workflows and interpretation. This research aims to fill these gaps through 1) increasing knowledge of pGSR and OGSR preservation, transfer, and persistence, 2) developing reliable screening methods for GSR detection, and 3) developing interpretation tools for forensic laboratories.

First, three studies were conducted to understand and model GSR behavior for collection, preservation, transfer, and persistence. The first study assesses the persistence of pGSR and OGSR over time using synthetic skin and GSR standards with known concentrations and particle counts to model GSR behavior. The synthetic skin model and GSR standards have been previously validated by our research group and tested in a similar study. One hundred and eighty samples were collected at various post-deposition times (i.e., 0, 2, 4, 8, 10, and 12 hours), and both pGSR and OGSR were detected up to 12 hours post-deposition.

The collection and preservation of pGSR and OGSR are crucial when addressing laboratory backlogs and understanding OGSR evidence, as immediate analysis of GSR samples is not realistic. Storage time, storage condition, and analytical workflow were assessed to determine the stability and preservation of pGSR and OGSR evidence. The findings demonstrate that the detection of pGSR and OGSR was unaffected by time for up to six months and workflow, and also recommend freezer storage for the preservation of OGSR.

The transfer and persistence of GSR in arrest situations complicate the interpretation of results for forensic analysts, since police often participate in arrests and are exposed to GSR. Therefore, this study aimed to understand the behaviors of pGSR and OGSR during arrests and evaluate possible solutions to reduce GSR exposure risks for arrestees. Screening and confirmatory methods were used to gain a thorough understanding of GSR in low-, medium-, and high-contact arrests, where transfer may occur either after firing or during handling between the officer and the arrestee GSR loss was more likely than transfer as arrest activities increased; additionally, wearing nitrile gloves during arrests helped decrease secondary GSR transfer.

Second, an investigation into using a Raman spectroelectrochemical method (Raman-SEC) as an emerging screening technique for OGSR analysis. A method was developed and validated for the analysis of diphenylamine (DPA), a common stabilizer, in smokeless powder. The application of the method was proven to be selective for DPA, as characterized by the unburnt and partially burnt smokeless powder, corroborated by LC-MS/MS and electrochemical techniques.

Finally, Bayesian networks (BN) were developed as an interpretation tool for activity level propositions using in-house data as a proof of concept. Additionally, a survey was conducted to assess how everyday activities (e.g., washing your hands) affect the transfer and persistence of GSR. The BNs were evaluated by analyzing the probabilities for each hypothesis and the likelihood ratios of mock case scenarios.

Overall, the development of rapid screening tools, the application of statistical methods using Bayesian Networks, and growing knowledge of GSR collection, preservation, transfer, persistence, and analysis are expected to revolutionize current methods for analyzing and interpreting gunshot residues. Additionally, it offers forensic laboratories more tools to make informed decisions about implementing screening methods and interpretation tools.

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