'Hide and seek' fingermark development on leather: visualisation and species differentiation on leather

The identification of individuals can be established via the uniqueness of fingermarks. While crime scene fingermarks can be plastic, patent or latent, the predominance of the last of these means that development methodologies for their visualisation are critical. Quite generally, selection amongst the numerous processes available is dependent upon target surface characteristics, such as porosity and colour, and environmental exposure conditions. Despite the availability of a number of techniques and reagents, some surfaces remain “problematical”. A prominent example is leather, which is widely encountered in casework associated with violent crime (weapon sheaths, holsters, restraints), wildlife investigations (skins, hides) and acquisitive crime (wallets, clothing). Accordingly, the overall aim of the present study is latent fingermark visualisation on leather surfaces.

Sub-categories of leather exist relating to source (fish, mammalian, reptile), authenticity (genuine or faux), physical surface properties (embossed, textured, smooth) and chemical finishes (dyes, waterproofing, patent, pearlised). It therefore seems appropriate that “leather” be considered as a diverse family of surfaces, for which different reagents may be optimum for fingermark development. Here we report investigations into such variations using two well-established application methods (powdering and cyanoacrylate fuming) associated with two novel reagents (PolycyanoUV and FPNatural1), whose observation is associated with opposite ends of the electromagnetic spectrum (UV and IR, respectively) and different modes of interaction (excitation and emission). Practically, the attraction of PolycyanoUV is its “one-step” application and of FPNatural1 is its potential for eradicating background interference.

This presentation explores latent fingermark visualisation on diverse leather samples exposed to differing environmental conditions for varying time periods, in conjunction with reagent delivery mode and sequential treatment processing. These observations are supported by substrate microscopy in cross section and optical profiling in 2D and 3D, which reveal substantial variations in histological structure for bovine, caprine, cervine, ovine and porcine leathers. Further interesting insights include the distinction of leather from young and aged animals of the same species. The influence of these morphological differences on reagent efficacy will be discussed. Additionally, details will be included of a novel application method for FPNatural1.

These fundamental insights ultimately lead to enhanced success rates for visualisation of latent fingermarks on leather surfaces. These offer the prospect of outcomes that could assist in the investigation of many offence types and provide valuable forensic evidence on previously unusable substrates. Furthermore, the practitioner recommendations will significantly impact international Criminal Justice Systems.