Modified Practical Approach in Repeated DNA Studies of Biological Evidence of Sexual Assault

ABSTRACT

In some cases, the initial studies of biological traces collected by vaginal and anal swabs after sexual assault are unsuccessful and do not end in deriving the genetic profile of the perpetrator and explicitly proving the sexual crime. Here we present and compare a group of 133 samples from 65 cases of sexual assault, on which we carried out repeated studies, using DNA typing from vaginal and anal swabs. The initial studies of these materials had been unsuccessful and had not led to deriving the genetic profiles of the offenders. Based on the obtained results, we present an alternative practical approach to collecting the maximum amount of remaining biological material deposited on the swab handles to conduct repeated tests of vaginal and anal/rectal smears. The practical approach applied by us analyzes whole 2.5 cm fragments cut out from the middle third of the swab handles, where biological material from the entrance of the vagina or the anal sphincter could have been collected. This approach yielded a further increase in the overall rate of successful DNA typing of approximately 14% for vaginal smears and 8% for anal/rectal ones.

Keywords:

• forensic science
• forensic evidence
• sexual assault
• vaginal/anal swabs
• DNA
• STR
• Y-chromosome