A preliminary study on temporal processes of latent fingermark degradation: Aged vs depleted impressions

Latent fingermarks are dynamic and three-dimensional (3D) topographical structures that degrade over time due to natural aging and/or depletion of skin secretions from consecutive depositions. Being able to recognize either process by optical methods is challenging but crucial for potentially reconstructing a crime's timeline based on measurable data. This proof-of-concept study assessed two distinct chronomorphometric techniques-3D-Sa (average ridge height) and 2D-BG (relative area of clear ridge detail)-to describe physical differences during the aforementioned time-dependent degradation processes. These metrics measured different aspects of ridge topography that were objective and analyzable. For 3D-Sa, a non-destructive optical profilometer was utilized, while conventional powdering with two distinct enhancers (i.e., BMP and TiO₂) was performed for 2D-BG. A total of seven independent and standardized experiments were combined involving 63 different participants (33 males and 30 females), generating 2,106 fingermark images. Ridge impressions were prepared under controlled pressure on glass microscope slides and aged in darkness in a monitored indoor environment. Both metrics successfully detected changes over time and across successive depositions as well as between the two temporal processes, with 3D-Sa showing higher efficiency in some instances. The effectiveness of 2D-BG was clearly dependent on the developer type. While the study was limited by factors such as indoor conditions and the use of a single substrate type (glass), these results provided preliminary data into the strengths and weaknesses of 2D and 3D analysis for dating purposes. It also suggested the potential application of this method in forensic research and, theoretically, in crime scene reconstruction.