Changes in the Composition of Fingermarks and the Effect on Enhancement

Abstract

The goal of this research was to identify key compounds present in ozone-exposed and nonozone exposed fingermarks. The research also aimed to determine whether or not the change in fingermarks upon ozone exposure would affect enhancement procedures and if certain methods of enhancement could take advantage of those changes. Squalene, a long-chain, unsaturated alkene was targeted as a key component in sebaceous fingermarks as it is very prone to oxidation via the process of ozonolysis. A solvatochromic dye, Nile Red, was investigated as an enhancement technique, as previous research had identified a positive colour change interaction with lipid components. We were able to identify changes in squalene and fingermark components via ATR-FTIR and confirm that the squalene component of sebaceous fingermarks is susceptible to ozone degradation. Further investigation with GC-MS analysis provided identification of the compounds whose presence was indicated by ATR-FTIR. The sensitivity obtained with a ChromatoProbe direct sample introduction method helped to confirm that, after 20 min ozone exposure the squalene component of a fingermark had almost completely degraded to several oxygen-containing breakdown products. Fingermarks deposited by multiple donors on four different substrate types were stored for time periods from 2 hours up to 8 weeks. These fingermark samples were used to compare the effect ozone exposure had on the cyanoacrylate fuming and Nile Red staining enhancement techniques. The ozone exposure of fingermark samples was detrimental to enhancement with cyanoacrylate fuming followed by Basic Yellow 40 dye, on all substrates investigated. In comparison, ozone exposure of fingermark samples enhanced with Nile Red showed little to no decrease in quality of ridge detail. Further investigation into enhancement of ozone exposed fingermarks showed that Nile Red exhibits a solvatochromic colour change dependent on the change of environment caused by ozone exposure of fingermark samples prior to enhancement. Hyperspectral imagining of Nile Red stained, ozone-exposed and non-exposed samples increased the visibility of the changes seen with standard digital photography. Image processing of hyperspectral data allowed for visibility of fingermarks that were previously indistinguishable from the background a polyethylene substrate. For other substrates like glass and aluminium foil, fingermark ridge detail and differences between the ozone-exposed and non-exposed samples could be determined from the hyperspectral imaging. This research has shown that changes do occur to fingermarks upon exposure to ozone and these changes can be visualised or quantified using a variety of techniques. Nile Red is a potential enhancement technique that could take advantage of the changes that occur with ozone exposure. Modification of the staining solution, testing of other substrate types and optimisation of techniques could allow further developments in this area.