The Relationship of DNA Evidence to Prosecution Outcomes in Sexual Assault Cases

Author(s): 
Cross, T.P., Siller, L., Vlajnic, M. & Alderden, M. (2022).
Source: 
Violence Against Women, 1 – 23.
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Summary: 

This study examined the relationship between DNA evidence and outcomes of prosecution of sexual assault. Results suggest DNA evidence contributes to case progression but also is a result of it.

 

Expanded Abstract: 
Research suggests that DNA evidence from sexual assault medical forensic evidence kits (also known as rape kits) has the potential to influence the outcomes of prosecuting sexual assault (see, e.g., Campbell et al., 2009; Davis & Wells, 2019).  However, the analysis of the relationship between DNA and these outcomes is limited.
 
This study examined the relationship between DNA evidence and outcomes of prosecution of sexual assault. Researchers coded data from prosecutor and crime laboratory files for sexual assault cases referred to prosecutors between 2005 and 2011 in a metropolitan jurisdiction in the northeastern United States. Cases with a DNA match were significantly more likely to move forward and result in conviction, even with other predictor variables statistically controlled. 
 
Results from this study found that cases with a DNA match were significantly more likely to move forward in the criminal justice system. About three-quarters of cases with a DNA match resulted in a guilty plea or went to trial.  More than half of cases with a DNA match to the suspect led to a conviction, versus less than one-tenth of cases that were processed at the crime laboratory in which there was no DNA match to suspect, and less than one-fifth of cases in which there was no kit or the kit was not analyzed at the crime laboratory.
 
In sum, cases with a DNA match to suspect were significantly more likely to advance in the criminal justice system and to end in conviction. Almost three-quarters of cases with a DNA match to suspect were carried forward to a guilty plea or trial compared to less than a third of cases without a laboratory report and just 13.6% of cases with a laboratory report but no DNA match to suspect. DNA match to suspect had a dramatic relationship with conviction: over half of the cases with a DNA match to suspect ended in conviction compared to less than one-tenth of cases that were analyzed at the crime laboratory and under one-fifth of cases not analyzed at the crime laboratory. The odds of conviction were much greater when there was a DNA match.
 
The possibility of obtaining DNA evidence is a major reason why thousands of victims of sexual assault undergo forensic medical examinations every year. Their investment makes it even more important to understand the impact of DNA evidence in sexual assault cases. The findings from the present study strengthen the case for providing victims access to quality forensic medical examinations, for investing in crime laboratories’ ability to conduct effective DNA analysis, and for training prosecutors to use DNA results effectively.
 
(The expanded abstract is excerpted and adapted from the article cited above).
 
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