NIJ has released a report based on retrospective DNA testing of physical evidence that had been retained in homicide and sexual assault convictions that occurred during a 15-year pre-DNA time period in Virginia. The goal of the study, conducted by the Urban Institute, was to determine if modern DNA testing of probative evidence would confirm the original conviction.
For a variety of reasons (for example, the biological evidence was very old), the DNA testing in two-thirds of the cases yielded “indeterminate” results; that is, testing was not sufficient to determine if the DNA came from the convicted individual. With respect to homicides in the study, indeterminate results rendered the sample size too small for the researchers to make any meaningful conclusions regarding a potential wrongful conviction rate.
With respect to sexual assaults, more than half of the 422 convictions in the study yielded determinate results. In those 227 convictions, testing eliminated the convicted individual as the source of the DNA and may support potential exoneration in 8–15 percent of the convictions.
The study used a unique set of data created after the governor of Virginia in 2005 ordered the DNA-testing of all retained evidence in certain violent-crime convictions. As such, the data and the findings based on them have limitations that should prevent generalizations to other situations. The data were from one state, one time period (1973–1988) and only involved cases in which forensic evidence had been retained. That said, the findings represent one important piece of a growing body of evidence that explores the role of scientific research in the fair and equitable administration of justice in the U.S.
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