How DNA Evidence Works in Criminal Cases

Watching criminal procedurals on TV, you’ve no doubt learned that your genetic fingerprint is in your DNA. You leave this telltale stuff behind you in traces of your skin cells, saliva, and sweat.

With the use of DNA technology, solving cold cases and linking suspects to convictions (or exonerations) has become straightforward. However, there are numerous aspects to DNA collection and forensic DNA analysis that can raise questions when it comes to DNA profiles in the criminal justice system.

For legal advice about the admissibility and use of DNA evidence, talk to a criminal defense lawyer.

Common Misconceptions About DNA Testing

DNA refers to deoxyribonucleic acid, the genetic information for life. In forensic science, crime laboratories use DNA to identify potential suspects by the biological evidence they leave behind in blood, hair, and other biological material.

The Federal Bureau of Investigation (FBI) also maintains the National DNA Index System (NDIS). This DNA database is part of the Combined DNA Index System (CODIS). Law enforcement agencies use the database to compare DNA test results with those of arrestees, missing persons, and convicted offenders in criminal cases.

Criminal defense attorney Kush Arora of Price Benowitz law firm in Rockville, Maryland, regularly faces this 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.”

Just because a biological sample matches that of a particular suspect, it doesn’t mean the reason is that individual’s guilt. There are numerous aspects to the collection, processing, and analysis of a person’s DNA evidence that can raise doubts.

“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, stored, or tested at the crime lab 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.”

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Your DNA Can Be at the Crime Scene Without You

In addition, a little-understood facet of DNA analysis 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. This refers to 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, but she had contaminated the swabs before they ever left the factory.

Our DNA profile is everywhere. It travels with us and can be carried by others, such as healthcare providers and law enforcement officers. It was this last circumstance that nearly landed Lukis Anderson on death row for a violent crime he didn’t commit. He had crime scene DNA under the fingernails of the victim.

Fortunately for Anderson, records from a nearby hospital gave him a documented alibi: He had been admitted when the crime occurred. The paramedics who had treated Anderson earlier that day had also responded to the 911 call at the murder scene.

Much remains to be understood about how DNA transfers occur and their impact on the conclusiveness of a DNA match 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’re Facing a Criminal Investigation, Get an Attorney

If you have privacy concerns about how law enforcement agencies use your forensic DNA evidence or genetic material in the criminal justice system, contact an experienced criminal defense attorney.