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Title: Interactions between latent fingermarks, deposition surfaces and development agents
Authors: Bacon, Simon Richard
Advisors: Jones, BE
Ojeda, J
Keywords: Forensic science research;Fingerprints;Titanium dioxide;Scanning electron microscope (SEM);Fourier transform infrared spectroscopy (micro-FTIR)
Issue Date: 2012
Publisher: Brunel University School of Engineering and Design PhD Theses
Abstract: Fingerprints have provided a crucial source of forensic evidence for well over a century. Their power lies in an inherent ability for human identification and individualisation, which is based on two fundamental properties: uniqueness and lifelong permanence. Latent fingermarks represent by far the most evidentially common and challenging form of deposition, whereby an invisible copy of the unique friction ridge fingertip pattern is left as an amalgamated secretory residue on any surface that is touched. Dry powder dusting, the first and most iconic method for visualising or developing these deposits, was developed in the latter part of the 19th Century. In the period since, a great number of additional techniques, utilising physical, chemical and optical interactions in isolation or combined, have been devised for the same purpose. By selecting the correct technique in the correct order, it is now possible to extract significant print details from an unprecedented variety of surfaces. In the UK, such operational choices are recommended via Home Office issued protocol tables, which offer an optimum guide based on substrate type, substrate properties and fingermark conditions. Development technique specificity has improved in the last half-century alongside increased biochemical understanding of residue composition, however, the shear variety of potential deposition substrates that exist within a heavily industrialised world inevitably causes disparities in efficiency, even within single protocol classifications. These effects are compounded by the enormous potential for pre- and post-deposition residue composition variation, relating to donor factors (age, sex, diet, lifestyle, etc.) and time dependant changes (environmental, biological, etc.) respectively. As a result, routine technique application can cause sub-optimal development. This research utilises high resolution imaging and analysis techniques to demonstrate how subtle surface chemistry and topography features can selectively influence routine technique efficiency within a single protocol classification (smooth, nonporous plastics). Titanium dioxide, a widely used white pigment, has been shown as prevalent in a range of polymers following SEM and EDX analysis, either in a patchy or ubiquitous distribution. SEM analysis demonstrates a strong interaction between the pigment and carbon powder suspension, which causes detrimental overdevelopment effects in off-ridge areas. ToF-SIMS mapping of a Formica substrate places a significant amount of patchy distributed titanium dioxide in the top 30nm of the surface. Mapping also indicated the presence of an aluminosilicate pigment coating; however, it’s involvement in the possible surface potential or surface energy interaction mechanism is unknown The effects of linear surface features, which have previously been implicated in off-ridge cyanoacrylate overdevelopment on two operationally relevant polymers, were also analysed by creating a silicon wafer model for micro-FTIR analysis. Fingermark residues, including hydroxyl groups, have been shown to migrate significant distances along induced scratches in the model substrate over a 48hr period. It is likely that observed overdevelopment along large valley-like features (uPVC) and scratches (polyethylene) in the operationally relevant polymers is caused by a similar migration of residues.
Description: This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.
Appears in Collections:Brunel University Theses
The Experimental Techniques Centre

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