An investigation into the selective deposition of iron oxide wet powder suspension

Latent fingermarks are residue impressions left on surfaces touched by the fingertip which contains unique friction ridge detail. Latent fingermarks are invisible to the naked eye and usually require development to make them visible. Wet powder suspensions (WPS) are a paint-like fingermark development technique that are recommended in the Fingermark Visualisation Manual, UK guidelines. Problematically, relatively little is known on what factors influence the quality of development of latent fingermarks, when visualised with WPS’s. The aim of this study was to fill this gap in knowledge. There were six main objectives to the research project; to establish which type of sweat (eccrine, sebaceous or natural) developed most successfully with iron oxide WPS, to observe inter person consistency in participant development, to observe intra person consistency in participant development, to explore if one or more individual constituents commonly found in fingermark residue may be the cause of interaction, to establish if the age of fingermark affected the quality of development and, to investigate if substrate type influenced the quality of development. The objectives were achieved by applying a combination of phase 1 and phase 2 studies, which are often used when researching a new or relatively unknown fingermark development technique. The results from each objective would generate new knowledge towards a fundamental understanding of what causes the selective deposition of iron oxide WPS and, some of the variables that may influence the quality and consistency of development. This fundamental understanding is vital to be able to recommend the use of WPS to its optimum potential and, to improve the technique beyond its current capabilities. The overall results of this project showed that iron oxide WPS may have an affinity to eccrine residue but when held in place by water insoluble material from other residues or contaminants. There was considerable variation in the quality of development of participant fingermarks (inter and intra personally), suggesting that composition, quantity and distribution of residue impacted the quality of development. The individual constituents tested had varying results depending on the method. It appeared that, when able to persist during the development process, all constituents developed but with varying qualities. Visual analysis indicated that the quality of development improved with the age of the fingermarks however, statistical analysis indicated that there was no statistically significant difference. Furthermore, it was established that substrate type appeared to have some influence on the quality of development of both participant fingermarks and individual constituents.