A preliminary evaluation of the effects of aquatic environments on the recovery of fingermarks on porous substrates

Latent fingermark detection can become increasingly difficult in the weeks following deposition, due to chemical and physical changes influenced by environment. There has been increased research interest into ageing mechanisms of fingermark residue, however these studies have typically been conducted in dry, indoors conditions. Less information is available regarding degradation processes that may occur in scenarios involving water and the potential longevity of porous substrates under such conditions. A pilot study was conducted to investigate the performances of Oil Red O (ORO) and physical developer (PD) on samples submerged in different aquatic environments in a laboratory setting. Charged fingermarks from three donors were deposited on copy paper and immersed in either salt water or freshwater; still or with water flow. Samples were treated at multiple intervals (1, 12, 20 and 40 days) after submersion. Results showed that high quality of development could be achieved up to 40 days after immersion. The overall performances of ORO and PD were generally unaffected in the early stages of the study. Physical and chemical degradation of both latent residue and substrate were observed, which were increased by salt and water movement. While PD appeared to be less affected by potential chemical changes, it was less effective than ORO due to substrate degradation in moving salt water. These results present the first steps towards better understanding the practical effects of degradation processes specific to fingermarks on porous substrates underwater.