When Words Mislead: Replacing “Touch” and “Trace DNA” with “Transfer DNA”
by Jo Ellen Nott
The forensic community is experiencing a critical shift in how biological evidence is described in the courtroom. For decades, terms like “Touch DNA,” “Trace DNA,” and “Wearer DNA” have been staples of expert testimony. However, a growing body of legal rulings and scientific research tells us these commonly used terms carry unconscious stereotypes that can mislead jurors and threaten the integrity of criminal trials.
The primary issue with legacy terminology is the unsupported implication of action. “Touch DNA” suggests the specific mechanism of direct physical contact. However, forensic science has confirmed that DNA can move via secondary or tertiary transfer, e.g., shaking hands with someone who then touches a weapon.
When an expert witness uses the word “touch,” a juror naturally infers direct involvement. In the recent high-profile Bryan C. Kohberger case, the court declined to bar such terminology but asked that witnesses avoid terms like “touch DNA,” “contact DNA,” and “trace DNA” as much as possible and required a jury instruction if “touch DNA” is used.
Additionally, the label “Trace DNA” can lead jurors to assume the sample is necessarily tiny or “low-level,” even though DNA recovered in contact/transfer scenarios can sometimes be substantial and yield complete profiles. For example, an internal validation study described by Bode Technology authors reported full profiles from multiple commonly handled items and a jeans sample yielding more than 30 ng of total DNA – illustrating that “transfer” samples are not invariably “minute.” National Institute of Justice (“NIJ”) similarly defines “trace DNA” as small amounts of DNA left behind at a crime scene and treats it as a low-yield challenge. NIJ-funded research on “direct PCR” aims to maximize recovery by placing the swab or sample directly into PCR to avoid losses during extraction and quantification. But NIJ cautions that direct PCR is not uniformly better across item types, can introduce low-level contamination (reported in a small percentage of samples), and consumes the portion tested, meaning there may be nothing left for re-analysis unless material is deliberately set aside.
The term “Transfer DNA” is proposed as a neutral, all-encompassing alternative. It provides several advantages for legal proceedings. The first is scientific accuracy because it describes the presence of DNA without claiming to know the specific “mechanism of deposition” (direct vs. indirect). The second advantage is neutrality because the word transfer avoids implying “intent” or “action” by the defendant. Thirdly, the term transfer has a broad utility. It accounts for DNA found on clothing (formerly “Wearer DNA”) without making assumptions about who last wore the item.
By adopting the term “Transfer DNA,” forensic experts can align their language with the actual limitations of the science, ensuring that judges and jurors assign the appropriate weight to evidence without being swayed by biased terminology.
Sources: Forensic Mag; National Institute of Justice
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