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The trouble with “trace DNA” evidence

On Behalf of | Jul 11, 2023 | Criminal Defense

DNA or “genetic” evidence has revolutionized the way that forensic science is used in the courtroom, particularly when there’s a violent crime involved. These days, juries almost expect to see DNA evidence as part of the prosecution’s case – something that wasn’t even permissible before 1987 in the United States

Since that time, however, not only has DNA become accepted as a “gold standard” type of evidence in the courts, but science has advanced to the point where even minuscule amounts of genetic material can be detected on a victim’s clothing or body.

Therein may lie the problem. The use of trace DNA has sparked a lot of controversy in recent years, and not without cause.

Small amounts of DNA can travel far and remain in place for a long time

There have been numerous studies that show that tiny amounts of genetic material – from skin cells to saliva or semen – can travel quite far from its donor and remain in place far longer than most people realize.

Imagine this: You make a purchase in a grocery store and pay in cash. The clerk who takes your money and gives you change is wearing glittery nail polish that – because it is rough – easily picks up the skin cells and sweat that passed from your hands to your money. That clerk is later the victim of a violent assault as they went home. Your DNA is found on their fingernails, even though you were miles away and home in bed at the time.

Far fetched? Not really. In fact, research has shown that trace DNA from bodily fluids can even be transferred through washing machines and remain detectable later – something that wouldn’t have been possible even a few years ago.

The reality is, as one forensic scientist put it, “our ability to analyze may outstrip our ability to interpret” the actual meaning of trace DNA thanks to modern scientific capabilities. That’s why it’s so important to understand that genetic evidence can and should be challenged in court.