Research Projects Searchable Database

Project - The Effects of DNA Evidence on the Criminal Justice Process

Organisation: Queensland Police Service
Contact: Michael Briody
Phone: (07) 3364-6564
Email: m.briody@mailbox.gu.edu.au
Status: In Progress
Completion Date: 2005

Abstract

The Effects of DNA Evidence on the Criminal Justice Process

This research project is in conjunction with Griffith University’s School of Criminology and Criminal Justice and commenced in 1999. It is examining the effects that DNA evidence had on decisions in criminal cases, both in the investigations phase and in the courts. The effects are assessed within a context of other evidentiary and extra-legal factors that have a bearing on case outcomes. A sample of around 800 cases, considered solved by police and completed to the appeal stage in Queensland, was selected for examination. Approximately half of these cases utilised DNA evidence, while the other halt as a control group, did not. Cases were selected in four categories: sexual offences, serious assaults, homicides and property crime. Data on the cases were analysed using advanced statistical methods to construct models of court processes. Independent evidentiary and socio-demographic variables were correlated to court outcomes. This allowed an assessment of the strength of DNA evidence in comparison to other types of evidence, such as defendant confessions, independent witnesses’ testimony and fingerprint and photographic evidence. Predictor models were then developed to demonstrate how, given case characteristics, the addition of DNA evidence could alter court outcomes.

Findings to date: In nearly all sexual offence cases, DNA evidence was used retrospectively by investigators to confirm the arrest decision and to strengthen the case against the defendant. For sexual offences, DNA evidence emerged as a predictor of whether or not a case would reach court; it played a crucial role in jury findings of guilty and it was significantly associated with custodial penalties being imposed. It also correlated to a slight increase in sentence length. Incriminating DNA evidence demonstrated no significant effect on inducing pleas of guilty for sexual offences, serious assaults or homicide cases.

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