Connecticut Supreme Court

 In State v. Terrance Police, SC No. 20528, 2022 Conn. LEXIS 123 (scheduled for release May 10, 2022), the issue was whether “touch DNA” was good enough for probable cause to get an arrest warrant. Here is the important part of the decision saying it wasn’t.

[T]he DNA evidence used to describe the suspect was not a single source sample known to have come from the perpetrator. Rather, it was “touch DNA,” also known as “trace DNA,” from multiple sources that might or might not have come from the perpetrator—something the police simply had no way of knowing when they applied for the John Doe arrest warrant. Notably, the state has not identified a single case, and our research has failed to uncover one, in which mixed partial DNA profiles from touch DNA provided the description of a suspect in a John Doe arrest warrant. Touch DNA “is a term used to describe DNA that is left behind just by touching an object …. Notwithstanding its name, however, touch DNA does not necessarily indicate a person’s direct contact with the object. Rather, according to [experts], abandoned skin cells, which make up touch DNA, can be left behind through primary transfer, secondary transfer, or aerosolization.” (Internal quotation marks omitted.) State v. Dawson, 340 Conn. 136, 153, 263 A.3d 779 (2021). Even when a person touches an object, “DNA is not always detectable, meaning that it is possible to have someone touch an object but not leave behind detectable DNA because … some people leave more of their skin cells behind than others, i.e., some people are better ‘shedders’ of their DNA than others. There are also other factors that affect the amount of DNA left on an object, such as the length of contact, the roughness or smoothness of the surface, the type of contact, the existence or nonexistence of fluids, such as sweat, and degradation on the object.” Id., 154.
 
As a result, touch DNA “poses potential problems that are not present, or are less often present, with DNA obtained from evidence consisting of bodily fluids ….” 7 C. Fishman & A. McKenna, Jones on Evidence (7th Ed. 2019) § 60:9, p. 785. For example, “[t]ouch DNA will often be available in much smaller quantities than DNA extracted from blood, semen, or hair”; id.; and “the presence of touch DNA may often be far less probative of a defendant’s guilt than DNA derived from bodily fluids.” Id., p. 787. Indeed, “trace samples lack the clarity of the more straightforward DNA evidence that can lead to a clear match to a specific individual. An object is found at or near a crime scene. A technician swabs the object to test for that DNA. These trace samples are usually quite small, there is often more than one person’s DNA, and the evidence is of a much poorer quality.” B. Stiffelman, supra, 24 Berkeley J. Crim. L. 115. “When dealing with such small amounts of DNA, there is much greater ambiguity as to how the DNA ended up on the object. For example, the DNA could have been left by someone who touched the object, or even by someone who touched the person who then touched the object. … In short, small amounts of DNA can be easily transferred and [travel]. Because of this, finding someone’s DNA on an object is less significant to a determination of guilt or innocence of a suspect.” (Footnote omitted.) Id., 115-16. (Emphasis added.)