Fingermarks have been used by law enforcement agencies to identify suspects in criminal activity. Although fingermarks remain persistent over time, the degradation pattern of latent fingermarks remains unknown. Previous studies examined the morphology of friction ridges on a two-dimensional scale, but recently 3D technology has been employed to examine how the height dimension degrades overtime. The Sa statistic was formulated to monitor the aging process of friction ridge heights from 6 donors. Fingermarks were deposited on two nonporous substrates (glass or plastic) and aged under dark or light exposure for 98 days. Pressure, time of contact, and treatment of finger prior to deposition were held constant while temperature and humidity were monitored throughout the study. Experimental variables included substrate and light exposure. Females exhibited slower degradation than males. For fingermarks deposited on glass, faster degradation was seen under light exposure. This finding was consistent for fingermarks deposited on plastic, but instrument contamination may have been possible. Slower degradation was seen on glass under both light exposures. This study indicates the Sa statistic is valuable for assessing fingermark degradation of friction ridges. However, due to a small sample size and variability in the rate of degradation between donors, genders, under different lighting and substrate conditions, the age of latent fingermarks cannot be determined at this time.
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