Purpose: After sexual assault there is a limited amount of time before the DNA evidence on the surface of the victim's body is not recoverable. During an assault, the offender may leave saliva on the victim's skin. Traditional examination methods use a swabbing technique to collect saliva for DNA testing. Victim activity, especially hygiene activity such as showering, may negatively affect DNA recovery.
Methods: In this experiment, we compared two techniques for recovery of salivary DNA from the skin's surface after a victim showers. We compared the traditional swabbing method to a "wet-vacuum" method using the M-Vac© to collect saliva from four body regions (neck, arm, stomach, and leg). In our research, we tested whether either collection technique obtained enough salivary DNA for autosomal and Y-STR analysis. In addition, we tested whether the M-Vac© is more effective at collecting DNA from large surface areas than traditional methods, by determining the amount of DNA collected.
Results: With both collection techniques, we were able to obtain male salivary DNA from at least one body region of the female after she had showered. There was no statistical difference in the amount of DNA collected between the swabbing technique and the M-Vac©. Autosomal STR analysis failed to detect the male contributor's DNA; therefore, we used Y-STRs. With Y-STR analysis, 47 samples returned a full male profile, and 26 samples returned a partial male profile after sample concentration.
Conclusions: This research shows that salivary DNA can be collected from skin after showering and successfully analyzed using Y-STRs.