Sexual assault forensic medical examination: is evidence related to successful prosecution?

We describe the medical-legal findings in a population of adult sexual assault cases assessed in an emergency department setting and reported to the police, document the law enforcement and legal disposition of cases seen over the study period, and determine whether medical-legal findings are associated with filing of charges and conviction after adjusting for demographic factors and assault characteristics.

This was a retrospective chart review of all police-reported cases seen from January 1993 to December 1997 at the British Columbia Women's Sexual Assault Service, a 24-hour hospital-based emergency service. Information on patient demographics, assault characteristics, and medical-legal findings was merged with data extracted from police and court files on the cases' legal outcomes and sperm-semen test results of collected forensic evidence. Cases were assigned a clinical injury extent score reflecting the degree of documented genital and extragenital injury. The association of medical-legal variables, patient demographics, and assault characteristics with filing of charges (among the subset of cases in which a suspect was identified by police) and conviction (among the subset of cases in which charge were filed) was examined by using logistic regression.

Charges were filed in 151 (32.7%) and a conviction secured in 51 (11.0%) of the 462 cases examined in this study. Genital injury was observed in 193 (41.8%), and sperm-semen-positive forensic results were obtained in 100 (38.2%) of the 262 samples tested. A gradient association was found for injury extent score and charge filing in the following categories: mild injury (odds ratio [OR] 2.85; 95% confidence interval [CI] 1.09 to 7.45); moderate injury (OR 4.00; 95% CI 1.63 to 9.84); and severe injury (OR 12.29; 95% CI 3.04 to 49.65). Documentation on the police file of receipt of forensic samples collected by the Sexual Assault Service examiner was also significantly associated with charges being filed (OR 3.45; 95% CI 1.82 to 6.56). Injury extent score defined as severe was the only variable significantly associated with conviction (OR 6.51; 95% CI 1.31 to 32.32).

The finding that documented injury extent had a significant positive association with both filing of charges and conviction is an important step in confirming the value of injury documentation in the forensic examination of sexual assault victims.