Touch DNA and Chemical Analysis of Skin Trace Evidence: Protecting Privacy While Advancing Investigations

37 Pages Posted: 18 Apr 2018

See all articles by Mary Graw Leary

Mary Graw Leary

Catholic University of America (CUA)

Date Written: 2018


Forensic science transforms criminal investigations by resolving previously unsolvable cases and bringing an increased sense of justice to communities. This application of scientific disciplines to legal questions aids investigators in solving crimes. While many sciences can be utilized — such as physics (pattern evidence), chemistry (toxicology), or biology (cause of death), to name a few — two aspects of scientific advancement have played an outsized role in responding to crime. Trace evidence analysis — specifically, deoxyribonucleic acid (DNA) analysis — is an essential component to an effective and accurate criminal justice system. DNA evidence has emerged as a powerful tool to identify perpetrators of unspeakable crimes and to exonerate innocent individuals accused of similarly heinous actions.

However, a different method of examining traditional trace evidence has quietly grown somewhat unnoticed. The emergence of so-called “touch-DNA” evidence and chemical analysis of skin traces represents powerful, novel uses of trace evidence that have significant implications for personal privacy. Furthermore, these abilities are developing within an outdated DNA jurisprudence that is wholly inadequate to protect individual privacy and facilitate the legitimate government interest in accurately investigating crime. Just as beeper and antiquated cellphone jurisprudence was an inadequate framework for the issues arising from smartphones or GPS tracking, DNA jurisprudence has failed to keep pace with modern uses of DNA.

This Article addresses touch DNA, chemical analysis of skin traces, and their implications for crime scene investigation, arguing that changes in how trace evidence is analyzed require alterations in the law’s approach to its use. Discussing the history of traditional DNA analysis, the article also examines the emergence of touch DNA and related technologies and how they differ from traditional DNA analysis. It analyzes new risks of these new technologies, specifically to suspects and victims of crime. Finally, it proposes a legal framework to address these privacy threats — drawing a distinction between the collection of DNA and cellular materials for identification purposes and a subsequent examination of these materials for other information about the source.

The framework adopted by the Supreme Court for cell phone examination in Riley v. California, required a more specific level of suspicion to examine the contents of a cell phone than to obtain it incident to arrest. This Article advocates utilizing this framework in the collection and examination of the even more personal information contained within DNA and cellular evidence. Specifically, it distinguishes between collecting the evidence and routinely testing it for identity and the more invasive examination of the evidence for additional personal information about the source. Before searching this deeply into this evidence for any information beyond identification, the government must establish a higher level of suspicion and obtain a warrant.

Keywords: DNA, touch DNA, California v. Riley, trace evidence, skin trace, privacy, Fourth Amendment, crime scene investigation

Suggested Citation

Graw Leary, Mary, Touch DNA and Chemical Analysis of Skin Trace Evidence: Protecting Privacy While Advancing Investigations (2018). William & Mary Bill of Rights, Vol. 26, Pp. 251-285, 2018., CUA Columbus School of Law Legal Studies Research Paper No. 2018-9, Available at SSRN:

Mary Graw Leary (Contact Author)

Catholic University of America (CUA) ( email )

116 McMahon Hall
Washington, DC 20064
United States

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