Revista de investigación forense

Changes in Yield of Contact DNA over Time after a Physical Assault

Abstract

Walter A Perez, Jillian Ng, Robert Oldt, William M Green, Edward Panacek and Sree Kanthaswamy

Touch DNA evidence can be defined as DNA resulting from the transfer of epithelial cells from skin to an object. Due to its high success rate in recent years, such as the JonBenet murder case and Waldo rape case, touch DNA evidence has been increasingly studied. Sexual assaults, which generally involve unwanted sexual contact between the victim and the offender commonly go unreported and often the perpetrator cannot be identified because of lack of evidence. This study aimed to determine how touch DNA collected from a victim’s wrist after a simulated sexual assault changed over time. Sexual assaults were simulated with male “assailants” grabbing the left wrists of female “victims” while they struggled to free themselves from the grip. Samples were collected immediately and at 15-minute intervals thereafter for 120 minutes after assault and then quantified using the Quantifiler® Duo DNA Quantification
kit. The maximum amount of male DNA obtained at time 0 was 10 pg/μL, which is below the quantification threshold of the Quantifiler® Duo DNA Quantification kit and detection limit of most commercial human STR identification kits. Although results here were limited by low DNA quantities and assay sensitivity, significant improvements can be made to better assay low template DNA.