Genetic genealogy brings promise and challenges to the Nancy Guthrie case

TUCSON, Ariz. – A cotton swab, a tissue and a pizza crust.

To investigators, the seemingly innocuous scraps were a treasure trove of DNA, helping to crack the cases of the University of Idaho murders, the Golden State Killer and the Gilgo Beach murders, authorities say, using a forensic tool called investigative genetic genealogy.

Investigators in the Nancy Guthrie case are hoping science can identify a suspect. But there are challenges.

Guthrie, the 84-year-old mother of “TODAY” co-host Savannah Guthrie, was reported missing on Feb. 1. Three distressing weeks have passed since her disappearance, and authorities have not publicly identified any suspects or persons of interest. Authorities have excluded the Guthrie family from the list of potential suspects, Pima County Sheriff Chris Nanos said.

Nanos, whose agency is leading the investigation with federal and state partners, said last week that mixed and partial DNA was found at Guthrie’s home. Mixed DNA is a forensic sample containing genetic material from more than one person.

More coverage on the disappearance of Nancy Guthrie

Some of that DNA found at the home does not belong to Guthrie, his family or anyone who worked at the residence, Nanos said.

“We think we may have some DNA there that could be our suspect, but we won’t know until that DNA is separated, sorted, perhaps admitted to CODIS, perhaps through genetic genealogy,” Nanos said Tuesday, referring to the Combined DNA Index System, the FBI’s DNA database of convicted felons.

But on Friday, he told NBC News that the lab that received the DNA reported “challenges” with the sample. He did not specify what the challenges are.

“We listen to our lab, and our lab tells us that there are challenges, and we understand those challenges, but our lab also knows that technology is changing so fast and with such a frenzy that they think some of these problems will resolve themselves in a matter of weeks, months or maybe a year, to allow them to do better with, let’s say, a mix of these kinds of things,” he said.

Nanos said he is “hopeful” that the samples will get to a point where they can be subjected to a genetic genealogy investigation or entered into CODIS, but “we’re not there yet.”

The sheriff’s department said in a statement Saturday: “As with any biological evidence, there may be difficulties separating DNA, etc. There are currently no updates regarding this process. »

Investigative genetic genealogy, or IGG for short, is a process in which unidentified DNA evidence is transformed into a digitized DNA profile. It then entered ancestry databases to find relatives, build family trees and narrow down the person behind the DNA. It has been used to solve unsolved cases, identifying unknown victims as well as killers.

The problem Nanos mentioned could relate to the DNA sample itself or the genetic genealogy investigation process, said Barbara Rae-Venter, a genetic genealogist who helped solve the Golden State Killer case in 2018 using the technique.

She said the sheriff’s comments suggest the DNA report contains too high a proportion of the victim’s DNA.

Colleen Fitzpatrick, an American genetic genealogist, said that when it comes to mixed DNA, the suspect must be the primary contributor.

“Say you have a mixture that is 90 percent Nancy and 10 percent someone else, that may not be enough for the lab to go ahead and get enough markers and do the identification,” Fitzpatrick said. “If it’s 50-50, it’s hard to split. Ninety, you can split that. The question is probably not just split, do you have enough DNA to work with anyway?”

The laboratory authorities allegedly used in the Guthrie case did not respond to a request for comment.

Challenges with IGG in the Guthrie case

Genetic investigators and genealogists may face several challenges in this case.

But mixed DNA, which is often found at crime scenes, can still often provide useful information, according to CeCe Moore, lead genetic genealogist at Parabon, a Virginia laboratory specializing in forensic genetic genealogy.

“We have had success in many cases of mixing,” she said. “But it takes a little longer, because there is an extra step. Once the profile we need for genetic genealogy is created, they then have to have the bioinformatics scientists work on that file to extract the suspect’s DNA.”

Moore said the discovery of mixed DNA gives him “hope” because “it seems more likely that he could definitely be linked to the kidnapper in this case.”

Nanos previously said blood was found on the porch outside Guthrie’s house and his DNA tested positive.

It takes about a day or two to build a DNA profile — and then “there are leads immediately,” said David Mittelman, a genealogist and CEO of Othram, a Texas forensic lab.

“In the worst case scenario, it will connect you to a very close relative, and in the best case scenario, it will connect you to your person,” he said.

IGG can also provide other information such as biogeographic ancestry, meaning the person’s historical origin, and link them to large family groups in certain areas of the country, Mittelman said.

Moore says how quickly this process is effective depends on race and ancestry.

“If the person of interest, in this case, has deep roots in the United States and is a white person, they could be identified within minutes or hours,” Moore said. “The vast majority of people in the databases we have access to have primarily northwest European ancestry and deep roots in the United States.”

But she said there is far less representation in databases of people with recent immigrant ancestry or those born outside the United States.

“If it’s someone who doesn’t have ties to the United States in their tree in more recent generations, it could take a lot longer,” Moore said.

This was the case in identifying Bryan Kohberger, who killed four University of Idaho students in 2022. It took several weeks because he had recent ancestors from Italy.

Access to records is also difficult for certain racial backgrounds, notably African-Americans.

“Emancipation is a brick wall,” Rae-Venter said. “The actual written records of these marriages and deaths, which we normally use when we try to build these trees, there’s no record once you hit the wall of slavery. You can’t go back further than 1863.”

Access to databases

Then there’s the question of how many profiles genetic genealogists can compare.

They’re limited to fewer than 2 million profiles to go through — even though more than 50 million people have taken direct-to-consumer DNA tests, Moore said.

Indeed, major companies such as Ancestry DNA and 23andMe, popular ancestry research sites, have barred law enforcement from accessing their databases to protect user privacy. However, these records can be requested by law enforcement, and these companies can be compelled to do so by court order or search warrant. The databases they can use are GEDMatch and FamilyTreeDNA, which have a membership capability allowing law enforcement to compare profiles.

“The two databases we’re allowed to use are two of the smallest databases. If we could use Ancestry, 23andMe or even MyHeritage, those databases would be huge. You’re talking 10 to 20 times as many people,” Rae-Venter said.

“If you’re working on something like the Kohberger case or the Nancy Guthrie case, time suddenly becomes very important. … It adds time to an already very lengthy proceeding,” she said of the database’s limitations.

Although the DNA samples in the Guthrie case don’t appear ready yet, experts are optimistic.

Rae-Venter said the IGG has been around since 2007, when it was more commonly used for cases of unknown parentage.

One of his first uses in a criminal case was to arrest Golden State Killer Joseph James DeAngelo in 2018. In 2020, he was sentenced to life in prison without the possibility of parole after pleading guilty to 13 counts of murder and 13 rape-related charges.

“At the time we made Golden State Killer, there were basically no tools to analyze the match information that you were getting, and now there are all kinds of very sophisticated tools to do that,” Rae-Venter said.

One of the advances lies in the possibility of working with smaller quantities of DNA.

“Back when we were doing this, it usually took about 200 nanograms of DNA. Now, I actually did a case with, I think we had 25 picograms, so it was basically 1,000 times less DNA,” she said.

She is optimistic that if enough DNA is collected, it could solve the Guthrie case.

“Assuming they managed to extract decent DNA from it, they should be able to identify a potential suspect. The problem is how long that will take,” she said. “But in the end, you should be able to solve the case.”

Marlene Lenthang reported from Los Angeles and Erin McLaughlin and Liz Kreutz from Tucson.

This article was originally published on NBCNews.com