Sexual assault is a heinous crime that as much as a quarter of women nationally experience in their lifetime. Not only do victims suffer the terror and degradation of the assault, but they are further at risk of injury and a range of difficulties with mental health and functioning. Survivors are also at risk of re-victimization from informal and professional responses that question their credibility and in effect blame them for the assault. In this difficult context, investigative methods that increase evidence against assailants while decreasing the burden on victims are especially important, and advances in the technology and expertise of collecting and analyzing injury and forensic evidence offer promise. The study: 1) examines the frequency of injury and biological evidence in sexual assault cases; 2) identifies case factors associated with the presence of injury and biological evidence; 3) analyzes how often biological evidence is processed prior to versus after arrest; 4) explores how injury and biological evidence as well as other factors are related to arrest; and 5) examines results for key comparisons thought to be salient for forensic evidence: Sexual Assault Nurse Examiners vs. other medical examiners; strangers vs. known suspects; child victims vs. adults and adolescents. This study merged data from three sources: 1) the Massachusetts Provider Sexual Crime Report (PSCR) database, 2) forensic evidence data abstracted for the study from the two crime laboratories serving the state, and 3) data on founding, arrests, and criminal charges from 142 different police agencies across the state.