Author ORCID Identifier

https://orcid.org/0009-0001-3046-5680

Semester

Spring

Date of Graduation

2026

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Forensic and Investigative Science

Committee Chair

Tatiana Trejos

Committee Co-Chair

Luis Arroyo

Committee Member

Monica Joshi

Abstract

During the discharge of a firearm, gunshot residue (GSR) is released and settles into nearby surfaces, leaving traces that can provide valuable information for forensic investigations. This study aims to improve understanding of the deposition, prevalence, and persistence of standard and less-lethal ammunition through an analytical framework that examines collection and analysis protocols, revealing connections among multiple traces for effective use in investigations and courtroom proceedings.

Research into the chemical residues of less lethal ammunition (LLA) is a critical frontier in shooting investigations. While standard leaded ammunition has over a century of established literature, the chemical fingerprints of LLA residues remain largely under-mapped, creating a significant gap. LLA is most frequently deployed in high-tension environments, such as crowd control or the immobilization of uncooperative suspects during arrest. As LLA becomes more accessible, forensic agencies must be able to link a suspect to a crime scene when traditional ballistic evidence is missing. For example, because LLA projectiles are often lighter and less aerodynamic than lead bullets, their residue dispersion patterns vary significantly.

Therefore, one goal of this project is to analyze and compare the composition of LLA with that of standard lethal ammunition, to develop recommendations for its use, and to increase awareness of the challenges in forensic investigations. The compositions of three LLA manufacturers are evaluated using a multi-technique approach, including Liquid Chromatography tandem Mass Spectrometry (LC-MS/MS) for OGSR, Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (FTIR-ATR), and microscope configurations, µ-FTIR for polymeric traces, and Laser-Induced Breakdown Spectroscopy (LIBS) and Scanning Electron Microscopy Energy Dispersive Spectroscopy (SEM-EDS) for pGSR. The experiments evaluate the likelihood of GSR transfer to the hands of a shooter, a bystander, and a simulated targeted person of interest (POI). The findings show that pGSR and OGSR deposit on the shooter’s hands, but indirect transfer to a bystander and a targeted POI is more likely for pGSR than OGSR. This exemplifies the complementary value of OGSR and pGSR, enabling more in-depth and practical interpretation of evidence under a relevant context. Moreover, the characterization of unfired components of the ammunition and the release of microscopic residues, such as rubber, pellets, cartridge cases, and bean bags, helps with source traceability (n = 60 hand-collected items and 9 fabric items). The LLA compositions (smokeless powders, primers, OGSR, and pGSR) are consistent with standard ammunition; however, traces from other polymeric and fabric components are distinctive of LLA. The study underscores the importance of comprehensive approaches to investigating whether LLA was properly used, minimizing the risk of GSR contamination when restraining a POI, and guiding decisions about sample collection and evidence interpretation.

The second objective of this project is to evaluate the use of personal electronic devices (PEDs), such as phones and watches, as alternative sampling substrates for GSR when circumstances may lead to loss or contamination of other, more common surfaces. We hypothesize that PEDs can retain GSR because they are held in the proximity of the discharged firearm and act as digital proxies for the wearer's hands, often retaining particles longer than skin does, which is frequently washed or naturally sheds. Beyond mere presence, these surfaces allow investigators to connect activity hypotheses by linking different pieces of evidence: for example, detecting characteristic GSR on a phone’s casing can be corroborated by latent fingerprints or touch DNA from the screen to confirm the device's user. Moreover, digital evidence can provide an accurate time window for the shooting. This integration helps forensic experts go beyond simply identifying material sources and instead focus on the activity itself—questioning whether the user was actively firing at that specific time and place—thus effectively evaluating common alibis related to secondary transfer or accidental contamination.

The dataset consists of 180 PEDs held by a shooter at the time of discharge and sampled at multiple time intervals (t=0, 1, and 2 hours).  The analytical scheme includes LC-MS/MS for OGSR and SEM-EDS for pGSR to establish primary and secondary GSR transfer onto these substrates, using universal carbon stubs for collection. The findings indicate that pGSR and OGSR are transferred to the shooter’s hands, but differences are observed on PED substrates. For example, pGSR is transferred either directly or via secondary contact onto a PED, whereas OGSR is less likely to transfer. A background study of phones and watches from a population that hadn’t recently used firearms indicates that pGSR and OGSR occurrence are generally low, adding significance to the findings.

Overall, this project offers several recommendations regarding the sampling and analysis of GSR evidence in complex casework, including cases involving LLA or situations where hand-collected specimens alone can be questionable. Personal devices like phones and watches could be a valuable alternative to traditional sampling substrates, especially when a long time has elapsed since a shooting or when the risk of indirect transfer contamination is high.

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