Available online at www.sciencedirect.com
Forensic Science International: Genetics Supplement Series 1 (2008) 442–443 www.elsevier.com/locate/FSIGSS
Research article
Assessing trace DNA evidence from a residential burglary: Abundance, transfer and persistence Jennifer J. Raymond a,b,*, Simon J. Walsh c, Roland A.H. van Oorschot d, Peter R. Gunn b, Laura Evans a,e, Claude Roux a a Centre for Forensic Science, University of Technology, Broadway, Ultimo, NSW 2007, Australia Forensic Services Group, NSW Police Force, Clunies Ross Street, Pemulwuy, NSW 2145, Australia c Forensic and Technical Services, Australian Federal Police, GPO Box 401, Canberra, ACT 2601, Australia d Victoria Police Forensic Services Centre, Forensic Drive, Macleod, Vic. 3085, Australia e Centre for Forensic Science, University of Strathclyde, Glasgow G1 1XQ, Scotland, United Kingdom b
Received 17 August 2007; accepted 8 October 2007
Abstract The considerable identifying power of DNA can see it treated as an absolute form of evidence, rather than as any other trace evidence. This study aimed to provide data into the abundance, transfer and persistence of trace DNA, in a particular crime scenario—residential burglary. Background levels of DNA on common burglary entry points were found to be low, however transfer of DNA during the action of a break-in is also low. The ability to recover analyzable DNA from outdoor surfaces decreases rapidly over several weeks. # 2008 Elsevier Ireland Ltd. All rights reserved. Keywords: Trace DNA; Abundance; Transfer; Persistence; Burglary
1. Introduction
2. Methods and results
DNA has played a role in forensic investigations in only the last 20 years. The technology has progressed considerably in that time, however the interpretative framework on which this evidence is based has been somewhat neglected. Having data to give estimates on the properties of DNA as physical evidence will enable investigators and scientists to assess its value as evidence in a particular case. Combining the particular case circumstances with experimental data on these properties will provide a more grounded, Bayesian-type interpretation of a trace DNA profile. The specific crime type of residential burglary was investigated in this study, and the trace evidence characteristics of abundance, transfer and persistence of DNA were tested.
2.1. Abundance study
* Corresponding author at: Forensic Services Group, NSW Police Force, Clunies Ross Street, Pemulwuy, NSW 2145, Australia. Tel.: +61 2 9977 0173. E-mail address:
[email protected] (J.J. Raymond). 1875-1768/$ – see front matter # 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.fsigss.2007.10.040
This study aimed to determine the baseline level of trace DNA present at common entry points of residential burglary. Twenty-nine volunteer residences were selected in inner Sydney. Prior to the experiment, a survey of 100 burglaries was conducted to determine the most common entry points. From this survey, four to five areas (windows, doors) in each residence were swabbed using a double swab method. The swabs were extracted using a standard chelex method. Swab extracts were amplified using a monoplex kit as a screening tool (at 28 and 34 cycles), and then AmpFlSTR Profiler PlusTM (34 cycles). A total of 150 swabbed locations were tested. After screening all samples with extended cycling, 46 (31%) gave a positive result. Thirty-nine (26%) produced alleles after Profiler Plus amplification. These 39 positive samples came from 20 different premises. The study indicated that the baseline level of DNA on common entry points is relatively low. Windows are a common entry point for burglars, but have a low baseline level of DNA
J.J. Raymond et al. / Forensic Science International: Genetics Supplement Series 1 (2008) 442–443
443
Table 1 The percentage recovery of buffy coat and DNA control solution over time, comparing lab storage and outdoor deposits
DNA solution in lab (%) DNA solution outdoors (%) Buffy coat in lab (%) Buffy coat outdoors (%)
t=0
1 day
3 days
1 week
2 weeks
4 weeks
6 weeks
76.94 40.46 95.00 43.39
20.22 5.11 64.51 31.60
2.71 0.59 86.19 29.68
1.68 0.03 32.31 8.72
2.36 0 10.11 1.21
2.32 0 4.20 0
3.12 0 4.10 0
present compared to other surfaces, and may be a good target area for evidence recovery at a crime scene. Larger alleles were rarely present in the background samples, and therefore if they are found in a crime scene sample, may indicate a recent contact rather than ‘background’ DNA. 2.2. Transfer study The transfer study investigated the amount of DNA likely to be transferred during a burglary. Twenty volunteers grabbed a pre-cleaned hard surface (door frame) simulating a burglary for 1 min. The surface was then swabbed using the double-swab method, and a buccal swab collected from the volunteer. Volunteers were not asked to wash their hands prior to the experiment, but were surveyed as to the last time they had. The swabs were extracted with a standard chelex method and quantitated using SYBR green real-time PCR. Forty percent of the handled surfaces returned an amount of DNA, varying from less than 10 pg to over 200 pg. The study found that transfer is generally low, and the age and handwashing status of the donor were not significant factors in this small survey.
burglary. Aliquots of control DNA and quantitated buffy coat were deposited onto painted wooden window frames on the outside of a residential unit building. Deposits were also placed onto sterile glass slides, which were sealed in a dark cupboard inside the lab. The areas were swabbed at time periods after the deposition; from time = 0–6 weeks, with three replicates at each time period. The swabs were extracted using a standard chelex method, and quantitated using SYBR Green real-time PCR. Table 1 shows the decline in DNA recovery as a percentage of the original deposited amount. The ‘naked’ DNA in the control solution declined more rapidly than the buffy coat as expected. No DNA was recovered from the outdoor locations after 2 weeks. 3. Conclusion This research demonstrates trace evidence characteristics of DNA, being abundance, transfer and persistence, in the context of residential burglary. Providing data into the many variables involved in trace DNA analysis allows a more objective probabilistic approach to the interpretation of profiles, and assists the presentation of this evidence in court.
2.3. Persistence study Conflict of interest The third component of the research assessed the length of time it is possible to recover DNA from surfaces after a
None.
