Trends in analysis of gunshot residue for forensic purposes

Detection and identification of organic and inorganic components of gunshot residue are well established within forensic chemistry because of highly characteristic and uncommon features of the products of ammunition discharge at the time and place of a shooting incident in comparison to other materials present in daily life of people. Both types of residue play an important role in establishing various circumstances of a shooting crime, though the most vital one concerns the possibility of relating a suspect with the activity of shooting. In this aspect, solid, inorganic particles, nowadays called characteristic, have been utilized. Their specific features result from the primer mixture composition, including compounds of heavy metals, lead, antimony, and barium, and from the extraordinarily dynamic conditions of their formation, taking place at the moment of the primer detonation. Scanning electron microscopy and X-ray microanalysis techniques proved to be necessary and sufficient to reveal the content and the spherical morphology of the particles for this purpose. Recently, the recommendation that the potential for lead exposure be minimized was followed in the production of ammunition cal. 9 mm Luger, 0.40 S&W, 0.380 Auto, and 0.38 Special. These modern types of ammunition expel less characteristic particles, the identification of which can be a challenge for the examiners. At least two solutions to strengthen the residue identity are taken into account: additional insights into the internal structure of inorganic particles, e.g., by means of electron backscattered diffraction and focused ion beam, as well as complementary examinations of organic residues with sensitive mass spectrometric techniques.