An experimental study about the presence of selenium in inorganic gunshot residues (GSR)

Gunshot residues (GSR) are produced by the discharge of firearms, and often provide very important information in criminal investigations in cases involving the use of guns. Elemental analysis, performed by a Scanning Electron Microscope equipped with an Energy Dispersive X-ray Spectrometer (SEM-EDS), is the most discriminating method for characterizing inorganic GSR particles, and forensic procedures based on SEM-EDS are followed worldwide. The SWGGSR “Guide for Primer Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive X-ray Spectrometry 11-29-11” refers to “Gun bluing” but Se (and also Cr) is not included among those elements whose presence is allowed in particles which are “characteristic of GSR”, neither according to the SWGGSR guide itself nor the current relevant ASTM “Standard guide for gunshot residue analysis by scanning electron microscopy/energy dispersive X-ray spectroscopy” E1588-16. Whenever unusual elements are found in alleged GSR particles, a “case by case” approach is recommended, and suitable research and documentation is required. In the present paper the authors show evidences of the presence of selenium in lead, barium and antimony (characteristic of) GSR particles detected in casework by laboratories placed both in Europe (Italy and The Netherlands) and in Australia. Firearm bluing products containing selenious acid has been experimentally proven to be a reasonable source for selenium in inorganic GSR particles. For the first time, a case-by-case approach is adopted to support fruitful interpretation of GSR particles containing selenium.