Fingermark Development on Leathers: Visualisation and Species Differentiation

The uniqueness of fingermarks provides identification of an individual. In practice, most such marks are latent: selection of the optimum reagent to render them visible depends on the nature of the surface and the object’s history. Despite availability of many processes, some “difficult” surfaces with low fingermark recovery rates remain: leather is a prime example. The generic goal of this work is visualisation of latent fingermarks on leather surfaces relevant to acquisitive crime (bags, wallets, clothing), violent crime (belts, restraints) and wildlife crime (animal hide).

Although “leather” is commonly considered a sufficient description, there are many sources (animal species, “fake” leather), physical surfaces (smooth, embossed) and chemical finishes (unfinished, patent leather, dyes, waterproofing agents). Consequently, we consider “leather” as a family of materials, potentially responsive to different fingermark reagents. To permit exploration of these surface variations, treatment was focused on two well-established types of reagent, a powder and a cyanoacrylate, but as relatively new variants. First, we used FPNatural1, an infrared fluorescent powder. Observation in the near-IR region has the advantage of eradicating background interference. Second, we used PolycyanoUV, which has the advantages of a one-step delivery process and, to generate fluorescence, illumination in the ultraviolet region.

The presentation explores delivery modes and sequential treatments for the reagents and the results obtained from leather samples exposed to different environmental conditions for different periods of time. Microscopic observation (in plan view and cross section) reveals substantial variations in material structure for bovine, caprine, cervine, ovine and porcine leathers. The influence of these morphological differences on reagent efficacy will be discussed. These fundamental insights ultimately lead to success rates for visualisation of latent fingermarks that are significantly higher than generally reported. The outcomes could assist in the investigation of wildlife crime and provide valuable forensic evidence on previously unusable substrates.