Impact of forensic science on criminal justice system outcomes : how does chemical trace contribute?

The criminal justice system is expected to be fair and effective. Decades of research point to the critical role that forensic evidence may play in meeting this expectation. Yet this evidence base has focused almost exclusively on biometric evidence, and little is known about the efficacy or otherwise of smaller disciplines. The aim of this research was to explore the contribution that chemical trace evidence in particular may make in supporting police investigations and court processes in Victoria, Australia. Quantitative and qualitative data relating to the use and impact of chemical trace and other forensic evidence were collected in a series of three studies based on criminal justice system data and surveys of investigators. A quantitative analysis of criminal justice system outcomes revealed new insights into the role played by forensic science. In particular, it was discovered that the impact of forensic evidence varied between disciplines and that there are potential interactive effects of using multiple forms of evidence, which may enhance fair and just outcomes. This research has provided insight into the diverse and nuanced ways that chemical trace evidence is used in criminal investigations and pre-trial processes that lie beneath the observable impact on the judicial steps measurable using quantitative methods. Capturing qualitative data has proven essential for revealing the less tangible modes of benefit provided, which need to be recognised to appreciate the full value provided by this form of evidence. Chemical trace evidence in particular was found to influence the decision-making of investigators in a number of ways. This finding contradicts prevailing forensic community perceptions that the benefits of trace evidence are largely confined to its application in court. Knowledge of the use and impact of forensic evidence could be used by service providers to guide the strategic deployment of services and to optimise the support provided to police investigations and court processes. The findings in this research have implications for the effective use of chemical trace and other forensic evidence. The limited availability of empirical research on the value provided by many forensic evidence types is a current weakness in the effective utilisation of forensic science in the criminal justice system.