If you’ve followed the story of how investigators caught the Golden State Killer, perpetrator of one of the most notorious cold cases in U.S. history, then you might be under the impression that we’re living through a revolution in detection. Law enforcement identified Joseph James DeAngelo, who in 2020 pleaded guilty to 13 murders attributed to the GSK, using forensic genetic genealogy, a combination of DNA analysis and traditional genealogy. One of the key figures in that investigation was a 74-year-old retired patent attorney living a quiet life with her cats and her garden in Northern California, Barbara Rae-Venter. In her new book, I Know Who You Are: How an Amateur DNA Sleuth Unmasked the Golden State Killer and Changed Crime Fighting Forever, Rae-Venter recounts her work on the GSK and other cases, but as for the golden age of forensic genetic genealogy? As far as Rae-Venter is concerned, that’s already over, due to what she regards as onerous privacy protections—and the fact that this method’s breakout star seems oblivious to the way her work might be misused is a little alarming.
Amateur sleuths have earned plenty of derision in recent years, from the ghoulish TikTokers spinning out wild theories about Gabby Petito’s murder for clout to the online Nancy Drews who harassed an innocent neighbor of the University of Idaho murder victims because they considered his demeanor to be suspicious. Rae-Venter’s success may appear to validate the Miss Marple school of non-professional crime solving, but labeling her an “amateur” is more shrewd marketing than strictly accurate. True, she had no experience in law enforcement in 2015, when she was asked to help the San Bernardino County Sheriff’s department identify the biological relatives of a woman who had been abducted as a child, but Rae-Venter’s expertise in genetic genealogical investigation was already considerable. She has a Ph.D. in biology and her law practice specialized in biotechnology patents. Since her retirement she’d been volunteering for an organization that helps adoptees find their birth relatives. (Also, while she never mentions this in I Know Who You Are, she was married for 12 years to J. Craig Venter, who would go on to found the Human Genome Project in 1990.)
Genetic genealogical investigation uses DNA databases to find matches to an individual (who may be an adoptee, a crime victim, or a perpetrator). The matches tend to be distant—if the investigator is lucky, a second cousin. The investigator then turns to public records and other sources—such as newspaper reports, social media posts, and family trees posted by other researchers—to work backwards in time, seeking the most recent common ancestor of those cousins. This person will also be an ancestor of the target individual. Researchers then build out a full family tree descended from that ancestor. They search that tree for people who might be the target individual, narrowing down the candidates by location, age, and other details. If, for example, an infant was adopted in Arizona, they will focus on who among the match’s descendants lived in Arizona at the time the child was born.
Private companies like Ancestry, 23andMe, and FamilyTreeDNA provide DNA analyses to their customers for a fee and will match a profile to other profiles within their own service. Anyone seeking matches among all the DNA profiles out there would either have to join all of these services, paying for a new profile each time, or upload their profile to GEDmatch, an open-source database, in the hope that potential matches who used a different private service would do so as well. GEDmatch played an instrumental role in identifying DeAngelo, both in narrowing down the list of suspects to six men and also by means of an eye-color prediction tool that told Rae-Venter that the GSK profile indicated the man had blue eyes. DeAngelo was the only one on the suspect list who did.
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This discovery electrified Rae-Venter. She describes sitting in her office chair, staring at her computer screen, transfixed by the realization that, apart from the murderer himself, “I might have been the only person in the world who knew the precise identity of the Golden State Killer.” The passage reminded me of a scene in scientist Hope Jahren’s memoir, Lab Girl, in which Jahren describes how she felt on arriving at her first original experimental result, thrilling that “I was the only person in an infinite exploding universe” to know the product of an obscure botanical process. Rae-Venter’s discovery was the opposite of obscure, but the similarity in their accounts suggests that whatever her past professions, Rae-Venter is a scientist at heart, and driven by a scientist’s particular, almost possessive hunger for knowledge.
Knowledge, however, is not the same thing as wisdom. Throughout I Know Who You Are, Rae-Venter holds tight to “the DNA” and its ability to prove facts conclusively, but the human implications of these facts often slip through her fingers. In a remarkable story from her own life, she recounts how her father, a New Zealander named Jack Rae, was contacted by a man claiming to be his son. This jibed with a letter her father had received during World War II; the British woman he was engaged to wrote to say that she had borne him a son. After the war, however, Jack was unable to locate either his fiancée or the child, who had been adopted. Jack was thrilled to be reconnected with the first-born son he had always said he wanted. (Barbara was his eldest child with his wife.) The son, Robin, petitioned for New Zealand citizenship with Jack’s acknowledgement of his paternity.
Barbara would have none of this, and, in reviewing the citizenship petition, “crossed out all of Robin’s anecdotal evidence and added instead that he had to submit to a DNA test at his own expense before my father would agree to help him in any way.” The test revealed that Robin was not Jack’s biological son, but Robin somehow convinced Jack that the results were mistaken. The two men continued to proudly proclaim their filial relationship, attending a reunion of Spitfire pilots where “everywhere he went, my father proudly introduced Robin to everyone as ‘my son’ while forgetting to introduce me at all.” Barbara understandably found this “extremely hurtful,” but when she finally made the decision to alert New Zealand immigration officials that the paternity petition that Robin had submitted (and that Jack had signed) was false, she attributes the choice to her indignation on behalf of “the sanctity of DNA.” That her own motives might be more personal than high-minded doesn’t seem to occur to her, and she never reveals how her family responded when she informed on them—two peculiar omissions that point to a persistent blind spot.
More than once, Rae-Venter has found herself backfooted by the disconnect between the rationality of scientific fact and human beings’ emotional responses to it, as when she admits to being “unprepared” for the backlash against genetically modified foods. (She worked on the Flavr Savr tomato patent.) GMOs, she is confident, are safe, so what’s the problem? How, more than one reader will wonder, could she not see the negative response to them coming?
In Rae-Venter’s eyes, much of the outcry about the use of private citizens’ DNA profiles by law enforcement is similarly misguided. Hadn’t she and other researchers been using the same data to find the birth parents of adoptee for years, without any fuss? “It was a surprise to me that the use of the DTC databases and GEDmatch for investigative genetic genealogy would suddenly become an ethical issue,” Rae-Venter writes. Following this controversy, GEDmatch and other DNA services tightened their rules about allowing authorities to access their data, and when police do use the technique, as in the investigation of the recent murders in Idaho, there is what Slate’s Heather Tal Murphy describes as “an emerging trend of leaving out any mention of forensic genealogy from court documents and press conferences.” Hence, the end of the brief golden age of forensic genetic genealogy as Rae-Venter sees it, an idyll that lasted only as long as hardly anybody knew what investigators were up to.
I Know Who You Are is mostly a lucid and entertaining detective story, but if Rae-Venter’s memoir has an argument, it’s that this pullback is misguided. Wasn’t the quest to obtain justice for crime victims and yank dangerous criminals off the street an even worthier cause than reuniting adoptees and their birth families? Maybe. But just as consumers have ample cause to disbelieve large corporations who assure them that their products are safe, many people have excellent reasons to mistrust law enforcement.
Rae-Venter herself encountered an example of investigator bias in one of her partners in the GSK team, Paul Holes, the celebrated cold-case detective for the Contra Costa County Sheriff’s Office who has been the most visible face of the investigation. Holes initially insisted that the team focus on a man who matched his profile of the killer as a real-estate professional. He had less interest in DeAngelo, in part because he did not want to believe that a former cop like DeAngelo had committed such terrible crimes and in part because he had become very attached to the profile he’d created. (Holes glosses over this dispute in his own memoir, Unmasked: My Life Solving America’s Cold Cases.) Only when a DNA test of a close relative proved that Holes’ favorite suspect was not the GSK did he let it go. Rae-Venter recognizes Holes’ stubbornness as an example of “confirmation bias,” but doesn’t see that such biases are exactly the sort of thing that causes many people to doubt the police and hesitate to put more power in their hands.
The police detectives in I Know Who You Are, for the most part, resemble stock figures from crime fiction: committed and selfless truth-seekers who want nothing more than to close that one case that has haunted their entire career. Several of the investigators who requested her help were, like Holes, on the verge of retirement and couldn’t bear the idea of stepping away from the job without solving that last case. While a good deal of this is surely accurate, the resemblance to genre fiction tropes should give anyone pause. As with Jack Rae’s first-born son and Paul Holes’ profile, the human desire that something be true clouds our ability to detect when it isn’t.
Police detectives have their prejudices. They can become attached to their preferred narrative about a crime and will stick to it—sometimes even to the point of falsifying evidence. The very enemy that Rae-Venter’s father fought against in the 1940s stands as a reminder that governments can make malevolent use of their citizens’ genealogy, and more recent political events indicate that a descent into that kind of government is not at all unthinkable in the U.S. Based on I Know Who You Are, I would trust Rae-Venter when it comes to finding the facts. But deciding what to do with them calls for someone much less easily surprised by human nature and with a lot less blind faith in our institutions.