Investigating the position and level of DNA transfer to undergarments during digital sexual assault

Sexual assault cases are regularly encountered in forensic laboratories. The victim's underwear and other clothes are often submitted with the intention of retrieving the offender's DNA. We examined six sexual assault scenarios; removing underwear, removing brassiere, digital penetration of the vagina from the front, grabbing breasts over the top of the brassiere, digital penetration of the vagina from the rear, and grabbing the breasts under the brassiere from the rear. For each scenario we used a dummy weighing approximately 45 kg to mimic a victim and recorded where the underwear was contacted and how much DNA was transferred using volunteer ‘offenders’. We found that how much DNA was recovered depended on which individual acted as offender and suggest it depends on the shedder status of the offender. We also discovered instances of the spouse, or office co-worker of the offender on the underwear. The obtained results will assist in identifying areas to target on underwear for different sexual assault scenarios, and also will provide important information that can be used for assigning probabilities of DNA transfer aiding evaluations of forensic biology findings that consider activity level propositions.