Crime and Technology ·

Can Police Use Your DNA Test Without Asking You?

A kit under the tree tests one person and reaches every relative they have.

Unbranded DNA test kit in dark wrapping paper beneath a dim Christmas tree

By Jack Malacat

Content note: This article mentions cases of murder and sexual assault.

Somewhere under a tree this December, a box the size of a paperback will be waiting to be opened. Inside is a plastic tube and a promise about where your family came from. A friend of mine took one of these tests a few years ago and learned something the box never advertised: she had a half-brother. When she asked her mother, her mother confirmed it.

People who look up whether police can get 23andMe data usually want to know if the company hands its customers’ DNA to investigators. Its own guide says it uses every practical legal tool to resist police requests, and it releases a customer’s data only with that customer’s consent or when the law requires it. The catch is that you never have to spit in a tube to be found. Since 2018, investigators have identified suspects through DNA their relatives uploaded to genealogy sites that allow police searches, building family trees until the branches pointed at one person.

How a stranger’s family tree gets built

The method starts with whatever was left at a crime scene. A lab converts that DNA into the same kind of file a hobbyist downloads from a testing company, and investigators upload it to a genealogy site whose rules permit it. The site returns a list of people who share stretches of DNA with the sample, most of them distant cousins. From there the work happens in archives, among obituaries and marriage records. Genealogists trace each cousin back to shared great-grandparents, then forward again through every descendant, until only a handful of people fit the age and location of the person investigators are looking for.

The case that made the method famous broke in California in April 2018, with an arrest for murders and rapes committed in the 1970s and ’80s. The crimes had gone unsolved for more than three decades. The break came through a third cousin who had uploaded their results to GEDmatch, a free site where people compare DNA files from different companies, and genealogists built the tree from there. Over the following four months, at least a dozen more cases were reported solved the same way.

Could your family tree turn you in?

This is where the question reaches people who never bought a kit. In the fall of 2018, a team led by the computational geneticist Yaniv Erlich published a study in Science based on the DNA of 1.28 million consumer customers. Erlich was also chief science officer of MyHeritage, the company whose data the team analyzed. The researchers projected that about 60% of searches for a person of European descent would turn up a third cousin or closer, enough to start building a tree. They estimated that a database of about 3 million people could reach roughly 90% of Americans of European descent.

That reach isn’t spread evenly. Consumer DNA customers are overwhelmingly of European descent, the reverse of government forensic databases, where minorities tend to be over-represented. Whether you can be found depends on which families bought the kits.

A third cousin shares a set of great-great-grandparents with you. Most people couldn’t name a single one of theirs. It takes only one with a genealogy hobby.

Where your data actually lives

The 23andMe question became urgent in 2025, when the company went bankrupt. A court approved the sale of nearly all its assets to TTAM Research Institute, a nonprofit led by cofounder Anne Wojcicki, for $305 million. TTAM outbid Regeneron Pharmaceuticals, which had offered $256 million. The company had about 13 million customers, and TTAM promised to keep the existing privacy policies, including the right to delete your data. Five states still opposed the sale, Texas among them.

The sites investigators actually rely on made different choices. GEDmatch switched to opt-in in May 2019, and shortly afterward only about 50,000 of its roughly one million profiles had agreed to police matching. FamilyTreeDNA, which had opened its database to the FBI earlier that year, at first left American customers to opt out on their own. Its defaults have shifted since, which is worth remembering: these rules belong to private companies, and companies rewrite them.

I’ll be honest about where I stand. More of us live far from where our families started, and I think a genealogy record people can actually reach is a good thing to have. My friend’s discovery could matter in ways she hasn’t imagined. A half-sibling can never be a perfect bone marrow match, but has about a 50% chance of being a half-match, which transplant teams can work with.

My first reaction to this whole subject was that I’d only ever show up in a criminal investigation as the victim. That’s closer to the truth than it sounds, because victims are where this method does some of its most humane work. GEDmatch compares every kit, including those opted out of police searches, against cases trying to identify human remains. Still, the person whose relatives get searched never had to agree to anything. In 2019, law professor Natalie Ram warned that the country was drifting toward an informal national DNA database, and she pointed out that no one can sever their genetic ties to their relatives.

I still lean toward the open record. I also know the decision won’t be mine. It belongs to whichever relative mails a tube first.

Who in your family has already made that choice for you?

About the Author

one-man publication made possible with the help of AI. When he isn’t designing games or dreaming up new products, he’s here, chasing questions about the darker side of being human. He thinks the internet has enough AI slop, and he wants to show what these tools can do in the right hands, with the sources to back it up.

Sources and Further Reading

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