Prints in the Wild: Investigating Changes in Fingerprint Quality on Porous Surfaces Throughout the Day
Radford, Christopher Austin
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The purpose of this field study sought to determine the overall quality of the average latent fingerprint deposited on porous substrates, comparing it to that of a charged fingerprint, and also to investigate changes in said quality according to the time of day at deposition and activity prior to deposition. Research and validation studies of latent fingerprint processing techniques on porous surfaces predominantly use only charged fingerprints, which raises concern over the robustness and representativeness of such research as it relates to forensic evidence collected in the field. This study collected more than six thousand latent fingerprints in the field from nineteen male and female adult volunteers. Fingerprints of all ten digits were collected multiple times a day over the course of six days in booklets of white copy paper, wherein volunteers recorded the date and time of deposition as well as the most recent salient activity prior to deposition. The latent fingerprints were visualized with two different processing techniques: ninhydrin to develop the eccrine portion and Oil Red O to develop the sebaceous portion. Contrast quality and clarity of developed ridge detail was evaluated and statistical analysis was performed on the fingerprint data and recorded deposition information. It was determined that the average latent fingerprint deposited in the field is of distinct contrast quality upon visualization; however, the ridge detail clarity is very low, being unusable for identification. Furthermore, the overall quality of the sebaceous portion is notably lower than that of a charged fingerprint. While there is no significant linear correlation between either time of day or activity and the quality of a fingerprint, activities involving frequent, repetitive, and/or prolonged contact with another surface yield fingerprints most emulative of the average field fingerprint. These results not only confirm the difference between field and charged fingerprints, reinforcing the necessity to use fingerprints that are emulative of potential evidence in future research and validation studies of processing techniques, but also identify specific activities that can be implemented in the laboratory to produce representative fingerprints.