Yield of Male Touch DNA from Fabrics in an Assault Model

Abstract

Touch DNA evidence is increasingly being collected and analyzed during criminal investigations. The purpose of this study was to determine if a significant amount of male (suspect) touch DNA can be collected from the clothes of assaulted victims after varying time intervals. A “grab and struggle” model was used to transfer touch DNA materials from human volunteers onto three types of fabrics (cotton, polyester, and a cotton/polyester blend). This was designed to replicate a sexual assault, in which a male acted as an “assailant” and grabbed different fabric covered arm areas of a female volunteer “victim”. Afterwards, three cuttings from each fabric sample were taken and extracted at 12 hours and 7 days post-deposition. The extracts were then quantified using the Quantifiler®Duo DNA quantification kit. The maximum yield of DNA from cotton fabric 12 hours post-deposition was 7 pg/ul and 5 pg/ul for total human DNA and human male DNA, respectively. The limit of detection of the Quantifiler Duo kit is 23 pg/ul, therefore these results are below standard profile detection range. No significant deterioration of DNA yield between the two time intervals (12 hours and 7 days) was observed. Variation between the tested fabrics and the areas of sampling could not be determined due to the very small quantities measured. This study did not find useful amounts of touch DNA on clothes after this assault model. Results are limited by a relatively small sample size and the assault model parameters; however, these results do not support the routine use of touch DNA evidence from clothes in similar assault cases