Precision matters in science; both in testing and the words we use. Scientific terms are often replaced with simpler language and while that can make complex ideas easier to understand, it can also cause confusion.  This can happen in criminal investigations and forensic DNA testing where terms like touch, trace, transfer and contact DNA are sometimes used synonymously. They don’t all mean the same thing and using them incorrectly can change how a case is perceived. They can shape how investigators think about evidence, how attorneys present it and how juries interpret it.

A current example getting national attention is the case of Bryan Kohberger, the man who plead guilty to the murders of four University of Idaho students. A key piece of evidence is the DNA found on a knife sheath left at the crime scene. The DNA wasn’t from blood or other bodily fluids, it was from skin cells. This kind of DNA is often referred to as touch DNA, but should it be? Or is trace DNA more accurate? Some might even say transfer or contact DNA. 

The Science Behind the Words

At Sorenson Forensics, we typically use the term trace DNA on reports when describing low-level DNA that comes from skin cells left behind on an object, like the knife sheath from the Idaho case. Scientifically we can’t say with certainty that someone physically touched the object. DNA can be transferred indirectly, like from a person to another surface and then onto the item in question.

Calling it touch DNA implies a direct interaction that may not have occurred. That distinction is subtle but important. In court, saying someone “touched” something can suggest guilt even if the DNA got there by a completely different route.

That’s why forensic scientists are careful with language in technical reports and court testimony. Touch DNA is used in headlines and by the public, but in a scientific context, it can mislead.

Transfer and Contact DNA

Transfer DNA is used to describe DNA that’s deposited through indirect means, like if someone shakes hands with another person and that second person touches an object. The first person’s DNA might end up on that object without ever being near it.

Contact DNA is often used in the same way as touch DNA but again it’s not a term that confirms anything about how the DNA got there. It may result from direct handling or from indirect/secondary transfer, so the term itself doesn’t prove how the DNA ended up there.

In Court

These distinctions are important for law enforcement and legal professionals. The language used in reports, investigations and testimony can influence how evidence is received. Saying trace DNA leaves room for multiple scientific possibilities. Saying touch DNA may imply direct action that the evidence does not confirm.

Juries tend to give DNA evidence significant weight. That’s why clarity and accuracy are critical; not just in the lab but how results are explained and understood.

In the Lab

Here at Sorenson Forensics, we prioritize scientific integrity and transparency. When bodily fluids aren’t present, trace-level DNA can still offer valuable and investigative insight. But it’s equally important to explain what the DNA can, and cannot, tell us. We work closely with law enforcement and attorneys to ensure findings are interpreted correctly both in written reports and expert testimony.