Trace DNA evidence dynamics: An investigation into the deposition and persistence of directly- and indirectly-transferred DNA on regularly-used knives |
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| Affiliation: | 1. UCL Centre for the Forensic Sciences, 35 Tavistock Square, London, WC1H 9EZ, UK;2. UCL Department of Security and Crime Science, 35 Tavistock Square, London, WC1H 9EZ, UK;3. UCL Division of Biosciences, Medical Sciences Building, Gower Street, London, WC1E 6BT, UK;4. Office of the Chief Forensic Scientist, Victoria Police Forensic Services Department, 31 Forensic Drive, Macleod, Melbourne, Victoria 3085, Australia;1. Norwegian Institute of Public Health, Oslo, Norway;2. University of Oslo, Oslo, Norway;1. Department of Applied Science, Limerick Institute of Technology, Moylish Campus, Limerick, Ireland;2. Forensic Science Ireland, Garda HQ, Phoenix Park, Dublin 8, Ireland;1. Division Biological Traces, Netherlands Forensic Institute, P.O. Box 24044, 2490 AA, The Hague, The Netherlands;2. Swedish National Forensic Centre, SE-581 94, Linköping, Sweden;3. Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83, Linköping, Sweden;4. Forensic Science Ireland, Garda HQ, Phoenix Park, Dublin 8, Ireland;5. Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, P.O. Box 94248, 1090 GE Amsterdam, The Netherlands;6. Office of the Chief Forensic Scientist, Victoria Police Forensic Services Department, 31 Forensic Drive, Macleod, Vic. 3085, Australia;7. School of Life and Environmental Sciences, Centre for Chemistry and Biotechnology, Deakin University, Locked Bag 20000, Geelong, Vic. 3220, Australia;1. UCL Centre for the Forensic Sciences, 35 Tavistock Square, London WC1H 9EZ, UK;2. UCL Department of Security and Crime Science, 35 Tavistock Square, London WC1H 9EZ, UK;3. UCL Division of Biosciences, Medical Sciences Building, Gower Street, London WC1E 6BT, UK;4. Office of the Chief Forensic Scientist, Victoria Police Forensic Services Department, Melbourne, Australia;1. UCL Centre for the Forensic Sciences, 35 Tavistock Square, London, WC1H 9EZ, UK;2. UCL Department of Security and Crime Science,35 Tavistock Square, London, WC1H 9EZ, UK;3. National Institute of Criminalistics, Federal Police, SAIS 7, Lote 23, Setor Policial Sul, 70610-200, Brasília, Brazil |
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| Abstract: | Empirical data on the transfer and persistence of trace DNA are crucial to the evaluation of forensic DNA evidence. This evaluation can be complicated by the occurrence of indirect DNA transfer; the possibility of which is well established, but research into such transfer is often focussed on unrealistic situations, e.g. handling of DNA-free items after participants have shaken hands for 1–2 min. To simulate more realistic scenarios, this study investigated the deposition and persistence of both directly- and indirectly-transferred DNA on knives that had been artificially set up as ‘regularly-used’. Each knife was handled in a prescribed manner by a specific participant over two consecutive days to simulate regular use. Each participant then shook hands for 10 s with a fellow volunteer and immediately stabbed one of their knives into a foam block repeatedly for 60 s. DNA was recovered by mini-taping from triplicate sets of knife handles from four pairings of volunteers after regular use, and at one hour, one day and one week after the handshaking and stabbing events.Total amounts of DNA recovered from the knives, regularly used by a single person, varied among individuals; one volunteer consistently deposited significantly greater amounts than the others, whilst another volunteer did not always leave complete profiles. DNA attributed to the regular user persisted for at least a week, declining with increasing time between DNA deposition and recovery. Non-donor DNA was co-deposited at <5% of the profiles recovered, except for one volunteer, who consistently left DNA from their romantic partner on their knives at ∼25% and ∼11% of the profiles before and after the handshaking and stabbing events, respectively. In three pairings of volunteers, after the handshaking and stabbing events, alleles that could be attributed to the respective handshakers’ profiles were detected as partial minor profiles, equating to ∼10% of the profiles recovered. For the fourth pairing of volunteers, only complete single-source DNA profiles matching the regular user’s profile were recovered. However, it is important to note that, when indirectly-transferred handshaker DNA was detected, it declined with increasing time between DNA deposition and recovery.These data provide an initial insight into the detection and persistence of directly- and indirectly-transferred DNA that extend the data already available on forensic DNA transfer. The results herein suggest that the sooner an item is sampled after an offence has occurred, the greater the chance of recovering indirectly-transferred DNA, which has implications for forensic reconstructions. |
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| Keywords: | Forensic DNA analysis Trace DNA Transfer Persistence Regular use |
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