Latent fingermark degradation processes by <scp>3D</scp> imaging: The impact of substrate type and natural light on ridge height

Friction ridge patterns, including those from latent fingermarks, are valuable physical evidence in the identification of individuals in criminal and humanitarian investigations. Although latent fingermarks may persist over extended periods, their time-dependent degradation remains poorly understood. Traditionally, aging studies have focused on two-dimensional (2D) ridge topography instead of more comprehensive three-dimensional (3D) examinations; but recent technological advancements have enabled the analysis of ridge height (z-dimension) and its modifications over time as a morphometric to describe aging patterns. This study assessed a 3D metric, Sa (i.e., average surface height), to monitor the natural degradation process of fingermarks from six donors (three males and three females) over 3 months. These were deposited on glass and plastic substrates and exposed to either natural light or complete darkness indoors, with temperature and humidity monitored but not controlled. Results revealed a "substrate effect" with a faster ridge height decrease on plastic under both lighting conditions. Interestingly, a "light effect" was less noticeable, and mostly for the plastic substrate. Although not the main focus of this analysis, a "biological sex effect" was also noticed, where female fingermarks degraded more slowly compared with males. This study showed the potential of the Sa metric to characterize the loss of ridge height under various indoor conditions. However, due to limitations such as a relatively small sample size, a standardized and accurate age determination of fingermarks is not yet feasible. Further research is necessary to refine 3D examinations and develop reliable models for estimating fingermark degradation.