Developments in Detecting Recent Holding of Weapons

Joseph Almog, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel
Karni Lev Bar-Or, Herzliya Hebrew Gymnasium, Tel-aviv, Israel

Latent fingerprints and invisible impressions of firearms, left on the holders’ palms, are both distinct cases of Locard’s exchange principle: “Every contact leaves traces”.  Both are typical examples of circumstantial evidence that can prove a previous contact between an individual person and an object. Most handguns leave invisible impressions containing minute traces of iron on the hand. These impressions can be visualized by spraying with the chemical reagent 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT). From recent experience it is evident that clear, well-defined impressions, which are developed on the hands by the PDT reagent, can unequivocally prove recent contact with specific firearms, and even faint, nonspecific marks can at least allude to such contact. However, there are still many occasions in which the PDT reagent (marketed as Ferrotrace^TM or Ferroprint^TM) shows insufficient sensitivity. We found recently that a considerable improvement of the sensitivity can be achieved by exposing the palms to hot water vapors after spraying with the reagent. Another study dealt with weapons’ marks which are left on children’s hands. Throughout the world, young children are worryingly involved in both unintentional and intentional gun violence, rendering the forensic investigation of gun handling by children highly important. We found that counter-intuitively, children produce considerably more intense PDT impressions than adults. A plausible explanation which is based on physiological differences between children and adolescents is suggested.