Investigators are working through decades-old murders and rapes using a method called investigative genetic genealogy, which connects crime-scene DNA to people who have uploaded their own DNA to public ancestry websites. The work starts with a DNA sample left at a crime scene that never matched anyone in the FBI's criminal database (CODIS). Instead of looking for an exact match to a known offender, analysts upload a profile of that unknown DNA to a consumer site and look for the people who share enough DNA to be distant relatives, usually second, third, or fourth cousins. From those partial matches, a genealogist builds family trees backward and forward, then narrows the branches by age, sex, location, and other case facts until one person is left to investigate.
The case that brought the method into public view was the Golden State Killer. On April 24, 2018, California authorities arrested Joseph James DeAngelo, a 72-year-old former police officer, and charged him in a long string of murders and rapes committed in the 1970s and 1980s [1]. Investigators had uploaded crime-scene DNA to GEDmatch, a free public site where people compare DNA they originally tested elsewhere, found distant relatives, and built family trees that pointed to DeAngelo [1]. They then collected DNA he discarded, from a car door handle and later from his trash, and matched it to the old evidence [2]. DeAngelo later pleaded guilty and was sentenced to life in prison.
Two sites have done most of the heavy lifting in these cases: GEDmatch and FamilyTreeDNA. Both let users upload raw DNA data and see lists of genetic relatives, which is the exact feature a genealogist needs. The large consumer companies, including AncestryDNA and 23andMe, do not allow this kind of law-enforcement searching and have said they require a court order before turning over any customer data. That is why the public, upload-it-yourself databases became the working tool for cold cases, and why much of the privacy argument centers on them rather than on the bigger-name testing kits.
After DeAngelo, the pace picked up fast. One of the most visible practitioners is CeCe Moore, who in 2018 began leading the genetic genealogy unit at Parabon NanoLabs, a Virginia company that takes cold cases from police departments [3]. Parabon announced that its genetic genealogy service produced 10 solved cases in its first 100 days [3]. Moore's work also produced the first case of this kind to reach a jury. William Earl Talbott II was convicted in 2019 of the 1987 murders of Tanya Van Cuylenborg and Jay Cook in Washington State, the first U.S. murder conviction obtained with help from genetic genealogy [4]. That conviction was later overturned on appeal over juror bias, a reminder that the genealogy supplies a lead, and the rest of the case still has to hold up in court [4].
Because the method was spreading faster than any rules governing it, the U.S. Department of Justice issued an interim policy on forensic genetic genealogy, announced in September 2019 and effective November 1, 2019 [5]. It applies to Justice Department investigations and to state and local cases that use DOJ money [5]. The policy sets several limits. Police must first run the DNA through CODIS and exhaust standard techniques before turning to genealogy [5]. The technique is generally reserved for violent crimes such as murder and sexual assault, and for identifying human remains [5]. And no one can be arrested on a genetic association alone; traditional follow-up work and a confirmatory DNA test are required [5].
Consent is the heart of the privacy debate. When someone uploads their DNA to find relatives, their genetic information also exposes information about parents, children, siblings, and cousins who never chose to take part. GEDmatch changed its terms in May 2019 so that user profiles default to keeping law enforcement out, and police can only search the kits of people who actively opt in [6]. Opt-in numbers have stayed modest relative to the full database, which limits how many cases the site can help with but also reflects that the choice is now explicit [6]. Critics argue that even an opt-in system pulls in non-consenting relatives, and that there are still few binding laws, as opposed to internal policies, on how far police can reach.
The technique keeps producing arrests in cases that sat untouched for years, including identifications of unknown murder victims as well as suspects. Supporters point to the obvious benefit: families get answers, and people accused of serious crimes are found through evidence they left behind. Skeptics counter that a useful tool is not the same as an unregulated one, and that the rules are still mostly voluntary policies set by companies and agencies rather than law passed by legislatures. A handful of states have started writing statutes, but coverage is uneven across the country.
For readers following true-crime cases, the practical takeaway is that a cold case is no longer frozen just because the DNA never matched a known offender. The science of comparing distant relatives, combined with old-fashioned family-tree research, has reopened files that detectives had given up on. The open questions are less about whether it works and more about where the limits should be: which crimes qualify, who gets searched, what consent means when DNA is shared across a whole family, and who writes the rules.
Sources
- NPR (April 27, 2018), In Hunt For Golden State Killer, Investigators Uploaded His DNA To Genealogy Site
- The Washington Post (April 27, 2018), DNA website GEDmatch was used to identify Joseph DeAngelo as suspect, police say
- Parabon NanoLabs (September 2018), Parabon Announces 10th Solved Case in First 100 Days of Snapshot Genetic Genealogy Service
- CBS News (July 2, 2019), First conviction made using genetic genealogy
- U.S. Department of Justice (September 24, 2019), Interim Policy on Emerging Method to Generate Leads for Unsolved Violent Crimes
- Wikipedia (GEDmatch privacy policy history, citing May 2019 opt-in change)