When DNA only tells half the story

DNA evidence is often treated as the gold standard in criminal investigations. However, recent forensic discoveries have revealed an important limitation: DNA analysis can identify a point of contact, but it cannot explain on its own how that contact occurred.

A 2026 study documented a contamination incident involving DNA recovered from a plastic bag that had enclosed human remains. The DNA profile matched a male police investigator.

The issue: the investigator had never attended the crime scene, entered the evidence storage facility, or visited the lab. Investigators concluded the DNA was likely deposited through indirect (secondary) transfer.

Secondary transfer is increasingly recognised in forensic science. Research shows DNA can move between individuals and objects through everyday interactions, influenced by contact, environment, and how much DNA a person sheds. In some cases, DNA can appear at locations a person has never visited.

Most people cannot account for the many ways DNA transfers in daily life, from shared surfaces to indirect contact. Yet criminal proceedings often expect individuals to explain exactly how their DNA came to be on an exhibit.

The absence of an explanation however does not mean DNA was deposited during an alleged offence. Suffice to say DNA can appear in unexpected places without direct involvement.

Specifically, we now know DNA can move via handling, clothing, or even gloves used during investigations.

While a person’s DNA may be correctly identified, a good defence solicitor should where instructed  challenge its evidential value due to uncertainty about how it was transferred.

Bottom line: DNA evidence—while powerful—is not infallible. The presence of DNA in one’s case is not the end of the story; rather it should be seen as the beginning of the defence’s forensic inquiry.

Understanding the difference between DNA identification and DNA interpretation is crucial in any criminal defence. Ensure you have a solicitor ready and capable to defend your side of the story.

Charged with an offence and worried about the alleged evidence?
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