How Precise is DNA Evidence in a Criminal Case?

It’s not as open-and-shut as you might think

In the world of lay science, we can feel pretty sure about some concepts. We don’t have to be able to pronounce deoxyribonucleic acid to understand that our genetic fingerprint is embedded in our DNA, and that we trail this telltale stuff behind us wherever we drop a hair or leave bodily fluids. As such, with the rise of DNA forensic testing, linking suspects to airtight criminal convictions (or exonerations) has become a straightforward process. Right?


Rockville criminal defense attorney Kush Arora, of Price Benowitz, regularly faces this public misconception. “There’s an assumption much of the time,” he says, “that if there’s DNA, that DNA must be correct. It can be frustrating.”

Wait, incorrect DNA?! But what about TV shows, like CSI?

“Fifteen years ago, when I had my first DNA case, it was not what it is now,” Arora says. “Technology is better, the matching of DNA is more sophisticated. There’s no question the science is good science. It’s an important tool from both sides; it can exonerate people who are wrongly accused, as well as support a conviction. But one of the practical issues we run into is how people understand it, what kind of weight they give it, when it may not be proper in every case.”

In other words, just because a DNA sample is a match to a particular defendant doesn’t implicate them. 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, 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,” Arora says.

As forensic science evolves, DNA information has been deployed in new ways to the criminal investigation process. One emerging field uses a DNA phenotype to compile a data sequence indicating probabilities about what a suspect, or even a victim, may have looked like. This information can be helpful in cold cases, like the New York murder investigation where the victim’s race was not easy to determine from the remains. The information may also be used to generate a “DNA Snapshot,” or composite image to potentially identify suspects.

Concerns about use of these genetic variants, which can range in accuracy, include questions of privacy rights, as well as the potential for racial profiling, particularly when it comes to facial details. At this point, Arora remains skeptical about widespread use of these tactics. “Where technology is concerned, it’s always like a cat-and-mouse game. We try something, and then there’s litigation about whether it’s good or bad,” he says. “There was a time when DNA evidence wasn’t used in court because it was unreliable, and look where we’ve come. So who knows what the future holds for these kinds of profiles?”

If you have a question about how DNA evidence may be utilized in a case you’re involved with, contact an experienced 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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