Transfer, Persistence and DNA Source Attribution of Trace Biological Material in Digital Penetration Assault Cases

The Uniform Crime Report definition of rape was updated in 2011 from an 80-year-old previous definition to include the following definition: “penetration, no matter how slight, of the vagina or anus with any body part or object, or oral penetration by a sex organ of another person, without the consent of the victim”. Penetration with any body part – specifically digital penetration (penetration with fingers) – is the subject of the proposed work. Digital penetration as a form of sexual assault has gained much attention recently in the media with the recent highly publicized case of Dr. Larry Nassar, Michigan State University and USA Gymnastics medical doctor. Digital penetration cases will be challenging due to the presence of trace amounts of male skin epithelial cells amongst an overwhelming majority of vaginal epithelia (digital penetration of a female by a male) and/or skin epithelia (digital fondling or assault to external vaginal areas). Not only is the amount of male epithelial cells a challenge in these cases, but it is also the nature of the epithelial cells themselves (i.e. shed skin cells). Only a handful of reports have attempted to evaluate the persistence of male profiles in digital penetration evidence and even fewer have evaluated the persistence of female DNA under the fingernails of male suspects. Additionally, no studies, with the exception of one case report, demonstrate the ability to also determine the source of that female DNA as vaginal secretions.
The goal of the proposed work is to develop a full analysis workflow to permit the identification and an evaluation of the bi-directional transfer (male suspect to female victim; female victim to male suspect) and persistence of trace biological material in digital penetration cases. In this study, an evaluation of the ability to obtain DNA profiles from trace biological material in digital penetration evidence will be performed, using both standard and enhanced STR typing strategies. The interval in which not only DNA profiles, but uniquely also body fluid identification, can be obtained from these samples will be determined. This work will result in recommendations for the forensic DNA and forensic nursing communities regarding the time interval, optimal sampling locations and possible analysis workflows for digital penetration samples. The flexible and customizable workflow that will be developed will provide operational laboratories with the ability to implement all or portions of this workflow into their existing capabilities.