Your DNA Goes Where You Don't

DNA transfer can erroneously link suspects to crimes

By Judy Malmon | Last updated on January 23, 2023

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Watching criminal procedurals on TV, you’ve no doubt learned that our genetic fingerprint is embedded in our DNA, and that we trail this telltale stuff behind us in traces of our skin, saliva and sweat. As such, with the rise of DNA forensic testing, DNA databases and genetic tests, linking suspects to airtight criminal convictions (or exonerations) has become a straightforward process. Right? Wrong.

DNA Linkage Does Not Equal Guilt

Criminal defense attorney Kush Arora regularly faces this public misconception. “There’s an assumption much of the time,” he says, “whether it’s on the part of a judge or a jury, that if there’s DNA, that DNA must be correct. It can be frustrating.”

In other words, just because a DNA sample matches that of a particular suspect, it doesn’t mean the reason is because of that individual’s guilt. There are actually numerous aspects to the collection, processing and analysis of DNA that can raise questions about the certainty of such a conclusion. “We’ve had cases thrown out for issues with DNA where there’s a match,” says Arora,” but the manner in which the evidence was collected or stored was faulty, or there’s an issue with the chain of custody—any number of things that could call into question the validity of the results.”

DNA Sources Beyond the Crime Scene

In addition, a little-understood facet of DNA science has to do with how DNA can travel, landing on an object that the source never had contact with. This type of DNA transfer was behind the so-called Phantom of Heilbronn, a suspected serial killer with a trail of more than 40 crimes throughout Germany, France and Austria. The DNA trail led to a factory worker who produced the swabs used to collect police DNA samples. She was never at a crime scene herself, but she had contaminated the swabs before they ever left the factory.

Our DNA is everywhere, and it can travel without us. One study found that as much as 75 percent of crime scene materials contained transfer DNA, sometimes carried from one location to the next. Another found that one in five people have someone else’s DNA under their fingernails at any given time.

It was this last circumstance that nearly landed Lukis Anderson on death row for a Santa Clara County murder he didn’t commit. His DNA was found on the crime scene, under the fingernails of the victim. Fortunately for Anderson, records from a nearby hospital gave him a documented alibi: He had been admitted at the time the crime occurred. The mystery of his itinerant DNA could best be understood by speculating that the same paramedics who had treated Anderson earlier that day had also responded to the 911 call at the murder scene.

Where DNA transfer is concerned, as with the Anderson case, much remains to be understood about how transfers occur, and what impact this has on the conclusiveness of DNA evidence found at a crime scene. For now, it seems that confirmation bias can be a substantial hurdle for juries to overcome, as Arora attests.

If you have a question about how DNA evidence may be utilized in a case you’re involved with, contact an experienced Oregon criminal defense attorney to make sure the matter is properly handled.

For more information on this area of law, see our overview of criminal defense.

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