Characterization of Modern Ammunition and Background Profiles: A Novel Approach and Probabilistic Interpretation of Inorganic Gunshot Residue

The National Crime Victimization Survey (NCVS) most recent data reported 480,000 firearm related crimes in 2016. During the investigation of these crimes, the detection of gunshot residue (GSR) is crucial and therefore, a commonly submitted form of evidence to forensic laboratories. The current guidelines for GSR detection require the identification of characteristic elements (typically lead, barium, and antimony in standard ammunition and a different combination of compounds for nontoxic ammunition) using Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS). Although, the SEM-EDS method is reliable, the data acquisition process is time-consuming. Moreover, the emergence of new types of nontoxic ammunition is changing what we know about elements that are present in a GSR particle.

The research proposed will be two-fold to address the limitations in current GSR examination. The first is the qualitative and quantitative characterization of modern ammunitions using highly sensitive instrumentation to establish the ground truth about the elemental composition of both standard and non-toxic primers. The second part is an extensive population study of low and high-risk background populations (i.e., professions and hobbies which may mimic the presence of GSR), and a set of samples from known shooters who fired standard and non-toxic primers. The samples will be analyzed by SEM-EDS and by an alternative novel form of analysis proposed as a fast screening test (Laser-Induced Breakdown Spectroscopy, LIBS), which has been recently developed and validated in our research group.

A comprehensive population study will generate the data necessary to use machine learning algorithms to provide a probabilistic assessment of the evidential value of GSR. The sampling size of these populations has been estimated using power analysis (p=0.95) and a data set of 112 samples characterized by LIBS in our pilot study. Upon completion of the research, the forensic science community will have an updated list of elements present in modern ammunition, assessment of current methods and a rapid screening of GSR, and quantitative statistical interpretation of GSR evidence. As part of the dissemination plan, the results and data will be provided to the funding agency and shared with the scientific community, and strategic partnerships with GSR examiners will be established to evaluate the implementation of the proposed models. A study such as this will provide forensic examiners and the criminal justice with an essential leap of knowledge and the tools necessary to reach more definitive conclusions in the courtroom.

"Note: This project contains a research and/or development component, as defined in applicable law," and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14).

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