A Universal Method for the Detection of Organic and Inorganic Gunshot Residue based on Fast Fluorescence Mapping and Raman Spectroscopic Identification

Gunshot residue (GSR) is a type of trace evidence often associated with a violent crime. It has two subclasses - organic (OGSR) and inorganic gunshot residue (IGSR). Standard GSR analysis uses scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and focuses only on IGSR.  OGSR has garnered interest in the forensic community recently due to its superior recoverability at a crime scene compared to IGSR and potential to provide specific information about the ammunition used. The proposed work aims the development of a universal method for the detection and identification of both IGSR and OGSR on adhesive tape and directly on clothing material. This two-step method is based on fast fluorescence mapping for the detection of potential GSR particles followed by a confirmatory identification using Raman spectroscopy. The main product of the proposed study will be an optimized and validated protocol for the novel two-step method using a single spectrograph with a confocal microscope and mapping capabilities. A statistical model for the identification of both IGSR and OGSR based on Raman spectroscopic libraries built for most commonly used types of ammunition and firearms will be the main deliverable. When fully developed and validated, this novel universal method for GSR detection will be a significant asset for crime scene investigators. In addition, a proof-of-concept, fundamental study of the ability of fluorescence and Raman spectroscopy to determine the time since discharge based on GSR analysis is proposed. Specifically, the time range for GSR ageing and the probative value of IGSR and OGSR for determining the time since discharge will be investigated. If successful, this preliminary study will be a basis for a more rigorous investigation and method development in the future. This high risk and high reward study would offer a great utility for forensic science, since it would potentially allow for determining the time since discharge of individual GSR particles. The proposed study is a continuation of a long-term research and development program conducted in the PI laboratory in close collaboration with forensic scientists at the New York State Police Forensic Investigation Center in Albany and the Onondaga County Center for Forensic Sciences in Syracuse. Training the next generation of forensic scientists with broad background in spectroscopy and advanced statistical analysis is an important aspect of the proposed activity. During this three-year study, semi-annual reports and a final report will be produced. Anticipated products include conference presentations and publications.