Soil as an Unconventional Substrate for IGSR Detection: Does Dirt Matter?

The analysis of gunshot residue (GSR) is commonly utilized in the field of forensic practice to ascertain the occurrence of a shooting event. This is particularly important when the wound is no longer macroscopically identifiable, as is often the case in instances of advanced decay and skeletonization of the victim. However, it should be noted that GSR can disappear during decomposition. Moreover, in the case of a buried body, the issue of putrefaction is compounded by the additional challenge of contamination and weathering of GSR, especially inorganic (IGSR), by soil, depending on the specific burial environment. This context, although not uncommon, has been the subject of insufficient investigation. For this reason, a simulation of clandestine burials was carried out at the Forensic Taphonomy Facility of the University of Milan (Ticino-LEAFs) using piglets that had died of natural causes as a model of human decomposition. The cadavers were each shot twice with a Walther PP caliber 7.65 mm Browning, with one shot fired into the maxillary and one into the neurocranial portion of the skull. At predetermined intervals, the piglets were exhumed and autopsied, and IGSR samples were collected and analyzed by SEM-EDS. In particular, the analyses were conducted on the soil in contact with the anterior wound (both entry and exit), directly on the skull portions affected by the posterior gunshot, and on background soil samples. The study emphasized the necessity of critically and cautiously considering IGSR analysis, always referencing the specific physicochemical characteristics of the burial environment.