Evaluation of latent fingerprint storage conditions by friction ridge volume and clarity

The storage and preservation of latent fingerprint (LF) evidence prior to processing is vital to forensic investigations. This study introduces a method to objectively quantify the degradation of LF topography by examining the effects of four different temperatures (40, 22, 4, and -20°C) on LF volume and ridge clarity over 21 days. The goal is to determine the proper storage temperature for unprocessed LF evidence. In this case, two complementary methodologies are combined: an optical profilometer (OP) provides quantitative 3D measurements of LF volume (Vn-volume net) in μm³, while a traditional dusting method, with a titanium dioxide-based powder and subsequent analysis with LQMetric embedded within the Universal Latent Workstation (ULW), evaluates 2D ridge clarity and identifiable minutiae (BG-blue/green color area). The 3D metric provides quantitative data on temporal changes of LF volume that may otherwise be undetectable with the overlayed 2D color-coded maps generated by LQMetric. Statistical analyses of both datasets reveal significant differences in LF degradation across three of the four temperatures. It has been determined that 4°C is the best temperature for storing unprocessed LFs, as it results in the lowest ridge alterations over time. In contrast, 22°C (room temperature) is the most damaging condition. Interestingly, the levels of ridge preservation at 40°C and -20°C are equivalent, possibly caused by similar ridge "dehydration" processes that help to maintain ridge integrity. These findings provide initial data to standardize evidence storage conditions, enhancing LF potential for downstream examination.