Most sexual assaults that are reported to the criminal justice system are not prosecuted, in fact only 3 -26% result in conviction (Lonsway & Archambault, 2012). Additionally, the vast majority of reported sexual assaults are never referred by the police to prosecutors for arrest warrants and charges (Campbell et al., 2014; Spohn & Tellis, 2012). Researchers and policymakers have expressed concern that this long-standing pattern allows offenders to commit additional sexual assaults. Determining whether reported sex offenders commit other sexual assaults requires establishing linkages between cases. Typically, criminal history records are used to identify repeat sex offenders, but biological evidence in sexual assault kits provides another way to study how often sex offenders reoffend by linking DNA across multiple cases to the same perpetrator.

This study examined the forensic DNA testing results from a sample of over 7,000 sexual assault kits (SAKs) from Detroit, Michigan. Study researchers assessed how many SAKs yielded a DNA match to a reference sample in CODIS (the federal criminal database). They then assessed whether any linked case was related to another sexual assault.

Results showed that over one-third (35.7%) of the perpetrators in the study had two or more sexual assaults linked via DNA, a finding higher than prior studies that measured recidivism by reviewing court records (in those studies, recidivism rates range from 8-15%), in other words, criminal history records alone.