A criminalistic approach to biological evidence : trace DNA and volume crime offences
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Volume crimes such as burglary and street robbery present an enormous cost to the Australian community each year. These ubiquitous crimes traditionally have a low resolution rate, but the use of information gathered through DNA databases provides another avenue of investigation. The forensic response to these crimes could be increased with the use of trace DNA; however the lack of awareness of forensic science as a holistic discipline focusing on the study of traces, often leads to a lack of knowledge into the trace evidence characteristics of DNA. This problem is compounded by practical and interpretive difficulties. The main hypothesis tested through this study is that, with an increased understanding into the criminalistic properties of trace DNA, it may prove to be more useful and effective evidence in the investigation of volume crime than is currently the case. The project encompassed three parts. The first component was a detailed survey sent to every jurisdiction in Australia and New Zealand to benchmark methods and protocols, education and training of personnel, and opinions and uses of trace DNA. The second involved the analysis of the results of 250 trace DNA swabs collected from New South Wales crime scenes, in order to provide a comparison point to the experimental work. The final section comprised preliminary experimental work to investigate the abundance, transfer and persistence of trace DNA within the context of residential burglary and street robbery offences. The methods survey helped to identify methods to be used in the experimental component of the project, but also highlighted issues in the field including a lack of training and proficiency testing. The absence of data collation across the jurisdictions was also a point for concern, and prevented the identification of factors that may affect trace DNA success rates. The pervading outcome of the survey was the need for effective data management systems and strong communication lines to facilitate best practice. From the analysis of the casework data a success rate in the order of 15- 20% was identified for New South Wales trace DNA swabs, with an average of 1.7ng of DNA recovered. Subsets of the data were used to directly compare to the experimental results in terms of transfer and persistence. The experimental work gave an insight into the behaviour of trace DNA in crime scene scenarios. The level of background DNA on surfaces encountered in forensic investigations was varied; for example residential doors were found to hold more background DNA than windows. Whilst the level of DNA on personal items such as bags and wallets was found to be relatively high, DNA from the offenders of simulated robberies could still be detected in usable quantities on these items. DNA was found to persist in sheltered locations for at least six weeks,but declined more rapidly in outdoor environments, with profiles not recovered after two weeks. This information may help to assist the interpretation and presentation of trace DNA evidence when the judicial question is one of activity, rather than source. The data also may be used in the education of crime scene examiners to assist them to target the most probative evidential samples. With further work in this field, trace DNA will be more easily applied to investigations. Trace DNA may be a useful tool in volume crime investigations, but individual jurisdictions should assess their capacity to manage the evidence to ensure results can be disseminated and actioned in a timely manner, otherwise the investment may prove to be fruitless. Effective and ongoing training programs and functional data management systems should be implemented to maximise both the investigative and intelligence value of trace DNA evidence. A holistic approach to the implementation of forensic evidence, encompassing the groundwork of theoretical analysis, review of capabilities and logistical and technical improvements, would greatly increase its value in policing and the criminal justice system.
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