CeCe Moore, a petite woman with long thick curls of blond hair that fall well below her shoulders, sat on the sectional sofa crying. She’d been hired to connect DNA from a long-ago murder scene to a suspect. This is her sort of riddle, mixing genetics, census records, and Facebook friend lists. Moore is, in her own estimation, among the most experienced genetic genealogists in the world. No wonder she’d found him.

But the answer had been a surprise.

“I thought, it can’t be! This person could not have done this,” she says.

Moore was shaken. Someone had killed and drifted back into normal life, never expecting to be caught—not aware that, right now, she was studying him through her laptop.

Moore’s genetic sleuthing skills have been seen on PBS’s Finding Your Roots, on 20/20, and on daytime TV programs like The Dr. Oz Show, where she uses direct-to-consumer DNA tests to find the parents of adoptees, foundlings abandoned in dumpsters, and “war children” fathered during conflicts. She has solved hundreds of cases of unknown parentage.

This year the public learned of a startling new application of such genetic genealogy. In April, police in California revealed they had used a freely accessible collection of DNA profiles, assembled on a self-service website by genealogy fans, to find the Golden State Killer, a notorious serial rapist and murderer active in the 1970s.

Moore was not involved. But it was a break she’d been waiting for. Two weeks later, a company specializing in forensics, Parabon NanoLabs, announced it would form a “genetic genealogy unit” with Moore as its chief. Give Parabon DNA from an old blood stain or rape kit, and Moore will try to tell you who it belongs to.

In May, Moore fingered the killer in a 20-year-old double murder. It took her two days. She believes she knows the solution to several more murders. Announcements could come at any time.

Moore has no scientific degree. Like other prominent figures in the genealogy community, she is self-taught. She’s perfected a set of methods that she shares at conferences, in courses, and on a closed Facebook group, TheDNADetectives, which has 90,000 members. Many are adoptees or children of sperm or egg donors who are looking for their biological parents.

Genealogists build family trees. Are you related to Jesse James or Winston Churchill? Genetic genealogist do that too, but they use consumer DNA tests to accelerate the process. Once tiny, the DNA testing industry, made up of companies like Ancestry.com and 23andMe, possesses the profiles of more than 12 million people.

As the numbers grow, the possibility of remaining anonymous is evaporating. This is because your DNA is not entirely your own. Members of a family, even distant ones, share matching segments of genetic material. If Moore can find a match, she’ll be up in a person’s family tree in no time, filling in the blanks.

“If you are the perpetrator, I will find you from a second cousin.”

“If you are the perpetrator,” she says, “I will find you from a second cousin.”

DNA profiler

Moore lives in the hills outside San Diego. It’s a land of canyons, nature trails, and planned developments with upscale tracts of Spanish-style stucco-and-tile homes snaking along the canyon rims. Inside the house, it would be light, but Moore has the curtains drawn. She spends hours every day sitting in pajamas on the large beige sofa in the family room—her “spot”—unearthing the people behind the nastiest acts humans beings can perpetrate.

Her tools consist of a laptop, a wi-fi connection, a notebook, and—just added—a large whiteboard that sits on a stand in the dining area. On a recent day, a numerical case number was written across the top and a partial family tree, with birthdates next to each name, was sketched beneath.

Parabon, based in Reston, Virginia, offers police departments a $3,600 service called Snapshot. With DNA from an unknown suspect—the kind left at a crime scene in a blood spatter, under a victim’s fingernails, or on a cigarette butt—it can predict what that person looks like and create a drawing, similar to a police sketch. One sketch was so convincing that a 21-year-old Texas murderer turned himself in days after police showed it on TV.

Now the company is approaching police forces for which it has already created these genetic mug shots to offer them what Moore calls the “new package.”

Moore’s services are, essentially, the “package.”

Provided a DNA profile, she first assesses, on a scale of 1 to 5, whether or not genetic genealogy is likely to break the case. A 5 is nearly hopeless. A 1 is a sure bet. The ranking depends on factors like the quality of the DNA and what a quick search reveals about the number of matching relatives in a growing open database called GEDmatch. So far, Parabon has plugged 100 cases into the database, and Moore has been working on about 10.

Her first success came less than a month after the Golden State Killer was identified. It involved crime-scene DNA from an unsolved 1987 double murder near Seattle. Moore was given access to the DNA profile on a Friday. She turned in the answer Monday morning. It proved easier than expected. She had hits on both sides of the family. That let her triangulate to a couple with three daughters and one son. Process of elimination. It must be him.

Jay Cook and Tanya Van Cuylenborg were murdered in 1987. During a press conference in May, investigators in Washington State said genetic genealogy had pointed to a suspect in the cold case. Associated Press

In May, police arrested William Earl Talbott, 55, as he left work. His name had never before come up in the investigation. “If it hadn’t been for genetic genealogy, we wouldn’t be standing here today,” Snohomish County sheriff’s detective Jim Scharf said during a televised press conference. Moore’s face was projected on a video link behind him.

Heavy secrets

Moore got hooked on genealogy when she researched her own family years ago. Early on, genetic maps could only provide links to long-ago ancestors and historical groups. But by 2012, companies like Ancestry.com had begun employing advanced chips that read off half a million DNA letters across the chromosomes, making matches between relatives much more precise.

Moore developed a practice helping people track down sperm donors and mothers who’d given them up for adoption. She does not care that a man signed a contract with a sperm bank, or that a woman signed adoption papers. “A child is not party to that agreement,” she says. “I strongly believe each individual has the right to knowledge of their roots. When I learned there was a group of people denied access to that information, I felt it was a societal wrong. I wanted to do something about it.”

Moore is both an exposer of secrets and a keeper of them. DNA results let her see infidelity, or what is termed “mistaken paternity.” She is, in her free time, creating a database of incest. She says she has probably encountered more direct DNA evidence of incest than any other person in the world.

“There are really deep, heavy secrets people carry,” she says.

By last year, Moore understood something not widely obvious: that Parabon’s DNA results could also be entered into GEDmatch. The site has around one million profiles, uploaded by genealogists as a way to compare DNA results obtained from different commercial testing companies.

Unlike Ancestry.com and 23andMe, which do not permit police to search their databases, GEDmatch had, at the time, no clear rules on how investigators might use it. Moore believed she could solve murders. But she resisted the urge to probe the community database in secret. “On those nights, I couldn’t sleep because I wanted to do this so badly. If I was just anybody, I could have done it behind the scenes,” she says. “But I have been a community leader for years, and I am responsible for thousands, maybe tens of thousands, [of uploads] to GEDmatch.”

Then, in April, California police said they’d arrested the Golden States suspect. Prosecutors, in their news conference, indicated that “advanced” methods had been used. In fact, police had created a DNA profile and uploaded it to GEDmatch, exactly as Moore had imagined.

Debate erupted in the small community of genetic genealogists. Some could see nothing wrong with finding a killer. Others were alarmed that police had surreptitiously searched through a million of DNA profiles. To Moore, the wide publicity around the case was a green light. The secret was out. Those who objected could delete their profiles.

Finding a match

Moore’s first step in investigating a crime is to obtain from Parabon the DNA profile uploaded into GEDmatch. (After the Golden State case, the site updated its rules, formally allowing police uploads but only for “violent crimes.”) Moore’s odds of finding a genetic relative are fairly good. According to a mathematical analysis performed in May by Doc Edge and Graham Coop, who are geneticists at the University of California, Davis, the chance that an American of European background has at least one second cousin (and perhaps a closer relative) in a database the size of GEDmatch is 25 percent. For other races, the figure is lower. Both of the alleged killers caught using genealogy so far are white.

If Moore does find a person who shares DNA with the suspect—a “match”—she can guess how they are related. A parent and child share 50 percent of their DNA, first cousins share 12.5 percent, and so on. Once she has a match, she works backwards in time to locate ancestors from whom the suspect and the match are both descended.

Once she locates possible ancestors, she then moves forward in history, locating every child and every child’s child until the present. This process illuminates the family tree to which the suspect belongs. There is no CSI atmosphere, no multiple screens and large computers. It’s just Moore on the sofa toggling between sites like Newspapers.com and Classmates.com, school yearbooks, Facebook, and census records.