Will Your Genealogy Help Solve a Murder — or Get You Accused of One?

McKenna Princing Fact Checked
© CACTUS Blai Baules / Stocksy United

You send away for one of those mail-in DNA tests, spit in the tube, mail it back to the company and get your results, hoping to connect with members of your family tree or find out if you’re really a quarter Italian like your grandma claims. 

But instead of matching with a second cousin or great aunt, you match with a police officer.

That’s what happened in April 2018 when police used a genealogy database to identify a suspect in the long-cold Golden State Killer case. Police used DNA collected from a crime scene to find people with similar DNA, create a family tree and track down potential suspects.

It worked: Police identified and arrested Joseph James DeAngelo Jr., a former police officer, after he had been living under the radar for decades. He now faces more than a dozen murder and rape-related charges for crimes committed in the 1970s and 80s.

As one of the first major cold cases involving a genealogy database, the Golden State Killer case marks a turning point in the power of DNA to solve crimes. But the consequences of that power may not all be positive. 

How DNA is used to solve crimes

Amongst all humans, 99.9 percent of our DNA is identical. The differences in our DNA, called polymorphisms, are what make individuals unique and what make DNA testing possible. 

Finding a single polymorphism in DNA left at a crime scene and using it to try to match the DNA with a suspect isn’t effective, however, since family members and even strangers can share DNA markers. To be accurate, scientists examine at least 20 different markers before making any conclusions.

DNA’s stability makes it (when used correctly) highly effective for definitive crime-solving, says Celeste Berg, Ph.D., a professor of genome sciences at University of Washington School of Medicine. DNA that is sufficiently preserved breaks down very slowly, allowing plenty of time for analysis. 

DNA can be used for more than just proving someone’s guilt. Just this year, scientists were able to analyze 100-year-old DNA and identify the remains of the fallen Romanov family, who were killed in 1918.

The DNA sample doesn’t have to be as large as intact bones, either: a single hair follicle or skin cell will do. In the Golden State Killer case, police obtained DNA from the handle of DeAngelo’s car and a used tissue he had thrown into a garbage can.

Even partial DNA profiles can be used effectively by law enforcement, such as in 2010 when partial DNA was used to capture the Grim Sleeper serial killer.  

The ethical dilemma 

With great power comes great responsibility — and the potential for corruption. DNA is no exception. 

Aside from the fact that DNA samples can be rendered imperfect by contamination (accidental or malicious), there’s the question of whether or not it’s ethical for law enforcement to use something as personal as someone’s genealogic information without that person realizing. 

The third cousins with whom DeAngelo’s DNA matched probably had no idea their voluntarily uploaded DNA could be used to help implicate their distant relative. Nor did the two people who police first identified as suspects before police honed in on DeAngelo. 

“The ethical challenge is how to balance public protection with individual rights,” says Malia Fullerton, D.Phil., an associate professor of bioethics and humanities at the University of Washington School of Medicine. “Should police be able to so easily access databases? Most people say yes, especially in cases of violent crime. But where does privacy get to be overridden?” 

There are no clear answers, and opinions vary. But one important thing, Fullerton says, is transparency. 

Some companies that sell DNA kits or offer genealogy services don’t allow law enforcement access. Those that do need to be transparent about the possible unintended consequences of using their products. And law enforcement need to be transparent about what information they’re accessing.

Racial and other biases

Yet, even being transparent can’t change the fact that DNA analysis has other serious issues like racial bias. 

Oppositely, more people of European descent voluntarily submit their DNA to ancestry sites and genealogy databases. 

One major concern is that DNA can be used to convict innocent people and disrupt the lives of family who get drawn into the crosshairs. Due to the size of some online databases, family who haven’t had their DNA analyzed can be implicated just by association. 

One recent analysis estimated that, if just 2 percent of people in any given population submit their DNA to a database, those profiles alone are enough to identify at least a third cousin for nearly every person in that same population. 

That means you could be implicated by a third or fourth cousin submitting their DNA without your knowledge, just like in the Golden State Killer case.

Limiting the types of crimes for which DNA can be used as evidence can help prevent false convictions. In Washington state, for example, DNA is only collected for those convicted of felonies (think: murders, sexual assaults, robberies) and other serious offenses such as stalking or harassment. 

The takeaway

Before you purchase that DNA test, think about how your genetic information could be used. Are you OK with the fact that your genealogy could be accessed by police without your knowledge? No matter how you feel, there’s no right or wrong answer: The important thing is that you make an informed choice.