Little prior research has explored how prosecutors perceive and utilize biological and injury evidences in sexual assault cases. In this qualitative study, semistructured interviews were conducted with assistant district attorneys (ADAs) working in an urban district attorney's office in the northeastern United States. ADAs were asked to describe how biological and injury evidences could be probative and their strategies for using this evidence. The interviews suggest that prosecutors perceive the probative value of biological and injury evidences on a continuum, varying based on case characteristics. Prosecutors felt that undergoing a forensic medical examination in itself supported victims' credibility. Biological evidence bolstered victims' credibility if it matched the victim's account better than the defendant's. They perceived DNA evidence as helpful when it identified unknown suspects, confirmed identification of suspects by other means, or rebutted defendants' denial of sexual contact. DNA evidence was also helpful when victims were incapacitated, too traumatized to recall or talk about the assault, or too young to identify assailants, and when police used the information in interrogating suspects. The biggest limitation to biological evidence prosecutors cited was overcoming the consent defense. The ADAs reported they used DNA evidence even when it was not particularly probative, because it confirms the correct person is being prosecuted, it communicates the victim's and prosecution's seriousness, and it meets jury expectations in trials. Prosecutors found injury evidence useful because it corroborated victims' accounts and helped refute defendant claims of consensual sex. The findings may assist in educating others about biological and injury evidences in these cases, and could inspire professionals and advocates to work to develop and support a broad range of investigative methods.

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. Analyses suggest DNA evidence contributes to case progression but also is a result of it. These findings strengthen the case for quality forensic medical examinations, investment in DNA analysis, and increased prosecutor training.