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Touch DNA Evidence Collection in Sexual Assault Cases: Knowledge to Inform Practice

Event Dates
Event Duration
1 Hour

Touch DNA was a revolutionary concept when introduced in 1997. The application of touch DNA in sexual assault cases was tested in 2011 when evidence was collected in a groping sexual assault case. The victim was unable to identify the assailant, but both short tandem repeat (STR) and Y-STR DNA profiles of the suspected assailant were found from touch DNA samples collected from the victim’s body and clothing. This unique case resulted in practice changes and further research in this US Mountain West state. 

A summary of research and literature on factors associated with the development of touch STR DNA profiles will be shared. Prior research has found that some individuals are higher shedders of epithelial cells, resulting in greater likelihood of the development of touch DNA. Individuals’ actions, such as touching their bodies or hand washing, impact the amount of touch DNA deposited on items. The contact length of time and type of contact also influence the deposition of touch DNA. The substrate of the item touched affects the amount of residual epithelial cells; clothing has been found to have higher yield of touch DNA than skin. 

Research on DNA analysis findings from 31 groping sexual assault cases with evidence collected and analyzed found that 32% of the cases developed probative STR DNA profiles from touch DNA. Application of these findings to groping and other sexual assault cases will be discussed from a multidisciplinary perspective. These research findings along with the case study and literature review provide strong justification for touch DNA evidence collection and analysis in sexual assault cases. 

Dr. Valentine recommends education within the criminal justice system and with key stakeholders to provide sexual assault medical forensic examinations with evidence collection in groping sexual assault cases. She references the National Best Practices for Sexual Assault Kits: A Multidisciplinary Approach (2017) published by the National Institute of Justice as providing best practice guidelines for evidence collection and analysis of touch DNA in sexual assault cases. With the advancements in DNA analysis, touch DNA should be considered as potentially crucial evidence in sexual assault cases, especially groping sexual assaults. 

Reference: Valentine, J. L., Presler-Jur, P., Mills, H., & Miles, S. (2021). Evidence collection and analysis for touch deoxyribonucleic acid in groping and sexual assault cases. Journal of Forensic Nursing. doi:10.1097/jfn.0000000000000324 

Detailed Learning Objectives

  1. Attendees will be able to discuss factors that impact the likelihood of developing probative touch DNA profiles in sexual assault cases.
  2. Attendees will understand best practices for evidence collection for touch DNA in sexual assault cases.
  3. Attendees will be able to apply current research findings on touch DNA in sexual assault cases to multidisciplinary practice recommendations.

Date Created: March 24, 2023