Forensic genealogy helped catch killers. Can it find Nancy Guthrie’s kidnapper?
The sun was shining on the nicely maintained Sacramento neighborhood of Citrus Heights on April 24, 2018, and the California climate was living up to its golden reputation. But just outside a small home, a specialized team of police officers waited for its target, a serial rapist and murderer who had eluded capture for decades — the Golden State Killer.
Moments later, police tackled and arrested Joseph James DeAngelo, who later confessed to killing 13 people over 12 years in the 1970s and ‘80s. Investigators had been stumped for years after DeAngelo, a former police officer, left little evidence at the crime scenes. However, he did leave behind his DNA, the building block of an investigative technique still in its infancy when DeAngelo committed the crimes.
The DNA didn’t directly identify DeAngelo. But through an emerging field called forensic genealogy, investigators connected the samples collected from crime scenes to a relative of DeAngelo’s who had just completed an ancestry DNA test. From there, police linked the crimes to DeAngelo, allowing them to crack what had seemed to be an unsolvable case.
The arrest of DeAngelo, who is serving life in prison without the possibility of parole, has received renewed attention as authorities hope DNA evidence helps them solve another tough case: the disappearance of Nancy Guthrie, the mother of “Today” anchor Savannah Guthrie.
The FBI announced this week that DNA collected at the crime scene didn’t match samples in the bureau’s Combined DNA Index System, or CODIS. Nor did a sample taken from a glove found while authorities searched for the 84-year-old Guthrie.
Authorities are now reportedly turning to commercial DNA registries — such as Ancestry.com, GEDMatch and 23andMe — for matches. Searches of those databases might not find a match to Guthrie’s abductor, but they might turn up a relative — and, as in the Golden State Killer case and others, that might be enough.
How does DNA analysis work?
Crime investigators use several methods to analyze DNA evidence.
Jason Linville, the director of graduate studies in forensic science at the University of Alabama at Birmingham, said for traditional DNA testing, analysts must format the sample before submitting it to CODIS.
“Right now, the standard is they look at 20 areas within the DNA,” he told Straight Arrow News. “It’s those 20 pairs of numbers that are submitted to the database, and you either get an exact match or it doesn’t match anybody.”
Tracey Dawson Green, a professor of forensic science and chair of the Department of Forensic Science at Virginia Commonwealth University, said the system will sometimes find no matches. That’s what happened in Guthrie’s case.
“What the no-hit at CODIS simply means is that the individual who left DNA at the scene is not in CODIS,” she told SAN. “So they most likely do not have a felony conviction or been arrested of a qualifying offense in this country.”
But unlike traditional DNA testing, which looks for direct matches in criminal databases, forensic investigative genetic genealogy, or FIGG, goes deeper.
The process examines far more genetic markers and compares them to public genealogy databases. Dawson Green said the process can see far into a person’s family.
“Forensic investigative genetic genealogy queries many more sites along the DNA, and therefore it can be used to trace relatives generations away — third-, fourth-degree relatives,” she said. “That opens up a whole new avenue of identification by way of connection to familial samples.”
But FIGG doesn’t simply spit out a suspect. Instead, it gives investigators a list of people potentially related to the DNA sample. Analysts then create broad family trees that they whittle down until they get a definitive one.
How police caught the Golden State Killer
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If stored correctly in a cold, dark, and dry environment, DNA can be used for years or even decades.
DeAngelo committed his last major crime, the murder and rape of 18-year-old Janelle Lisa Cruz, in 1986. However, it took another 15 years for police to create a single DNA profile for DeAngelo’s string of rapes and murders.
The profile finally told authorities that the crimes associated with the Golden State Killer, the East Area Rapist, the Visalia Ransacker and the Original Nightstalker were all committed by the same person. Despite this major breakthrough, police still didn’t have a name.
That changed in late 2017 after police uploaded DNA collected from a decades-old rape kit into GEDmatch.com, a consumer website used to find relatives through DNA. They got a match, not a direct match, but they were closer to figuring out who the Golden State Killer was than ever before.
The DNA was linked to several of DeAngelo’s distant relatives, allowing authorities to create broad family trees. Police whittled the trees down until the last one pointed directly at DeAngelo.
However, police didn’t want to botch a major cold case, so they needed to be certain DeAngelo was their man. Investigators began monitoring DeAngelo’s home and collected new DNA samples from his trash and his car door. They compared those samples with the DNA recovered years ago and found it was a perfect match.
While the Golden State Killer case pioneered the technique, investigators in the Bryan Kohberger case modernized it.
In 2022, Kohberger murdered four University of Idaho students. Investigators were able to identify him as a suspect after they discovered DNA evidence on a knife sheath. Much like in Guthrie’s case, investigators found no matches in CODIS and began searching public genealogy databases. Analysts eventually narrowed the list of potential suspects.
When they got to Kohberger, investigators dug through his trash to find another DNA sample to test — and it matched the sample found on the knife sheath. The investigators later confirmed the match by taking a formal DNA swab test after Kohberger’s arrest.
“Once they get that DNA sample from the person and run it, then they know 100% whether it is or is not the person,” Linville said.
But the process can be time-consuming. In the Golden State Killer case, it took a few months of searching public databases before investigators found the genetic connection.
“Generating that profile in the laboratory, that can be done in a day,” Linville told SAN. “It’s the investigative stuff that’s going to take some time.”
When building a criminal case, DNA evidence alone can’t prove someone’s guilt. In Kohberger’s case, they also had cell phone data placing him in the area at the time of the crime.
“There’s going to need to be other investigative information to tie it all together,” in the Guthrie case, Dawson Green told SAN. “It’s not going to be a slam dunk, because there are other ways to explain away the presence of DNA in a room that have nothing to do with the commission of a crime.”
Are there drawbacks to FIGG?
One immediate issue with FIGG and the Guthrie investigation is that mixture DNA samples can’t be used in familial testing, according to Dawson Green.
“Mixtures are not viable samples for familial testing or genetic genealogy,” she told SAN. “In a home environment, you’re going to have mixtures. That’s very common.”
In the Guthrie case, investigators said that the DNA found in the glove was a normal sample and was submitted for FIGG testing. However, the glove was found miles away, did not match the sample found inside the home and was found along with 15 others. The FBI said the glove looked like the one seen by a man on Guthrie’s doorbell camera and was different from the others found.
Some have raised concerns about the potential privacy violations FIGG and other testing techniques could have. Critics say giving their genetic data to a company is dangerous. Hackers could attack the company, potentially compromising users’ genetic data. Authorities can also use public DNA databases, like GEDmatch, to develop a suspect.
Dawson Green argues that police using a public site to solve crimes is not problematic because users willingly upload their data and agree to law enforcement accessing it.
“It’s individuals that get those kits done, can download their data and then upload their data to a public database,” she told SAN. “When they do that, they have to now consent to being able to be searched against evidence samples for the purposes of crime solving.”
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Ella Rae Greene, Editor In Chief
