Is Your Third Cousin a Serial Killer?

Today’s article isn’t like most others. It’s pretty serious, actually. If you’re looking for a good laugh, just move on down the road. But if you want to read something interesting, keep going.


The website,, provides DNA and genealogy data for comparison and research purposes. It’s free to upload your information, but you have to subscribe to view your DNA matches. Members add their information from the genealogy sites Ancestry, 23 and Me, My Heritage, Living DNA, Whole Genome, and Family Tree DNA. After about two days, they can log back on and find their matches, if they paid for a membership. The site cautions that DNA is passed down on a random basis, so it’s not an exact science. Members can use GED Match to help an adopted child find biological relatives, or perform genealogical research.


You’re probably wondering why I’m writing about this website, and why you should care. But did you know that, for all the cases with DNA collected at the crime scene, law enforcement can solve 90% of them? The problem is that the databases only contain information for known criminals. If an offender has never been arrested, there is no DNA in the databases.


Thanks to GEDmatch, you can upload your DNA and authorize law enforcement to access your file. When law enforcement has a case with unidentified DNA, they can upload it to GEDmatch. The site will then compare the sample to members’ profiles. If there’s a match, then law enforcement receives a message. Remember, a member has to give permission for law enforcement to access their DNA. And they can only use the site to identify perpetrators of a violent crime. Violent crimes include murder, nonnegligent manslaughter, aggravated rape, robbery, or aggravated assault. Investigators can also use GEDmatch to identify human remains.


Have you heard of the Golden State Killer? Joseph DeAngelo avoided capture for over forty years, until the FBI used GEDmatch to convict him. DeAngelo used his skills as a former police officer to create clean crime scenes. His skills helped him kill thirteen people and sexually assault over fifty women. The police had DNA evidence but couldn’t match it to anyone in their criminal databases.


Fun fact—your DNA is roughly 50% similar to each of your parents, and 25% for your grandparents. The similarity for each generation is reduced one quarter, which means first cousins share about 12.5% of their DNA, second cousins 3.125% and third cousins less than 1%. Unless your close relatives are obsessed with their ancestry, it’s unlikely they are all in the database. But you can get thousands of third cousin matches. Investigators in the Golden State Killer case studied those third cousin matches.

But combing through third cousins was just the beginning. The FBI investigators tracked down records such as birth and marriage certificates, census data, and obituaries. And they used Facebook and other social media to fill in the blanks. The investigators combined all their information with the DNA profiles and built a family tree for third cousins of the Golden State Killer. This detailed process is called reverse genealogy.


The investigators identified potential suspects from their massive family tree and made a list. They narrowed this list by comparing the physical features to eyewitness descriptions. This last step gave them a small pool of suspects—a puddle, really. They narrowed in on Joseph DeAngelo.

The FBI placed him under surveillance and collected discarded DNA samples. Lab results proved DeAngelo’s guilt, and he is now in Corcoran State Prison serving thirteen consecutive life sentences. DeAngelo was the first, but he certainly isn’t the last. As of September 2020, GEDmatch is credited for helping to close almost 120 cold cases, and identifying eleven Jane and John Does across the United States.


You don’t have to join the police academy to bring a predator to justice. And you can do it in your comfy chair and snuggly blanket.


Jann Goar Franklin graduated Russellville High School in 1985 and lives in Grand Cane, Louisiana. She also writes books, which are for sale at You can reach her at