TUCSON, Ariz. — A Q-tip, a tissue and a pizza crust.To investigators, this seemingly innocuous trash was DNA-laden treasure, helping crack the cases of the University of Idaho murders, the Golden State Killer and the Gilgo Beach slayings, according to authorities, using a forensic tool called investigative genetic genealogy.Investigators in the Nancy Guthrie case hope that science can point to a suspect. But there are challenges.AdvertisementAdvertisementGuthrie, the 84-year-old mother of “TODAY” co-host Savannah Guthrie, was reported missing on Feb. 1. It’s been three agonizing weeks since her disappearance, and authorities haven’t publicly identified a suspect or a person of interest. Officials have cleared the Guthrie family as potential suspects, Pima County Sheriff Chris Nanos said.Nanos, whose agency is leading the investigation along 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 that has more than one person’s genetic material.More coverage of Nancy Guthrie’s disappearanceSome of that DNA that was found at the home doesn’t belong to Guthrie, her family or anyone who worked at the residence, Nanos said.AdvertisementAdvertisement“We believe that we may have some DNA there that may be our suspect, but we won’t know that until that DNA is separated, sorted out, maybe admitted to CODIS, maybe through genetic genealogy,” Nanos said Tuesday, referring to the Combined DNA Index System, the FBI’s DNA database of convicted criminals.But on Friday, he told NBC News the lab that received the DNA reported “challenges” with the sample. He did not elaborate on what the challenges are.“We listen to our lab, and our lab tells us that there’s challenges with it, and we understand those challenges, but our lab also knows that the technology is moving so fast and in such a frenzy that they think some of this stuff will resolve itself just in a matter of weeks, months or maybe a year, to allow them to do better with, say, a mixture of that kind of thing,” he said.Nanos said he’s “hopeful” the samples will get to a point where they can be submitted for investigative genetic genealogy or entered into CODIS, but “we’re not there yet.”Security camera video from the front door of Nancy Guthrie’s house. (Kash Patel via X)(Kash Patel via X)The sheriff’s department said in a statement Saturday: “As with any biological evidence, there can be challenges separating DNA, etc. There are currently no updates regarding this process.”AdvertisementAdvertisementInvestigative genetic genealogy, or IGG for short, is a process in which unidentified DNA evidence is turned into a digitized DNA profile. It’s then entered into ancestry databases to find relatives, build family trees and narrow down the person behind the DNA. It’s been used to solve long-cold cases, identifying unknown victims as well as killers.More in U.S.The issue Nanos mentioned could be with the DNA sample itself or with the investigative genetic genealogy process, said Barbara Rae-Venter, a genetic genealogist who helped solve the case of the Golden State Killer in 2018 using this technique.She said the sheriff’s comments suggest the DNA ratio has too high a proportion of victim DNA.Colleen Fitzpatrick, an American genetic genealogist, said when it comes to mixed DNA, the suspect has to be the major contributor.AdvertisementAdvertisement“Suppose you have a mixture and it’s 90% Nancy’s and 10% somebody else’s, that might not be enough for the lab to go forward and get enough markers and make the identification,” Fitzpatrick said. “If it’s 50-50, it’s hard to separate. Ninety-10, you can separate that. Probably also the question is not only separate, do you have enough DNA to work with anyway?”The lab that authorities are believed t …
