Ammunition Identification by Means of the Organic Analysis of Gunshot Residues Using Raman Spectroscopy

Abstract

The ability to unequivocally identify a gunshot residue (GSR) when a firearm is discharged is a very important and crucial part of crime scene investigation. To date, the great majority of the analyses have focused on the inorganic components of GSR, but the introduction of "lead-free" or "nontoxic" ammunitions makes it difficult to prevent false negatives. This study introduces a fast methodology for the organic analysis of GSR using Raman spectroscopy. Six different types of ammunition were fired at short distances into cloth targets, and the Raman spectra produced by the GSR were measured and compared with the spectra from the unfired gunpowder ammunition. The GSR spectrum shows high similarity to the spectrum of the unfired ammunition, allowing the GSR to be traced to the ammunition used. Additionally, other substances that might be found on the victim's, shooter's, or suspect's clothes and might be confused with GSR, such as sand, dried blood, or black ink from a common ballpoint pen, were analyzed to test the screening capability of the Raman technique. The results obtained evidenced that Raman spectroscopy is a useful screening tool when fast analysis is desired and that little sample preparation is required for the analysis of GSR evidence.