The Pima County sheriff investigating the disappearance of "Today" show anchor Savannah Guthrie's mother told NBC News it could take up a year to find a match for the DNA found at the scene.
Nancy Guthrie has been missing for three weeks, and investigators have not identified a suspect or developed leads on where she might be.
The FBI said Guthrie was last seen at her residence in Tucson's Catalina Foothills neighborhood on the evening of Jan. 31 and is considered a vulnerable adult who has difficulty walking, has a pacemaker, and needs daily medication for a heart condition.
Mixed DNA found at the scene has provided new hope that investigators could get a break in the case.
Sheriff Chris Nanos said some of the DNA does not belong to Nancy Guthrie, her family, or anyone who worked at her residence.
On Friday, he told NBC News he sent the DNA to the lab and said there were "challenges" with the sample.
"We listen to our lab, and our lab tells us that there's challenges with it, and we understand those challenges," Nanos said.
"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," Nanos added.
"As with any biological evidence, there can be challenges separating DNA, etc. There are currently no updates regarding this process," the sheriff's office said in a statement Saturday.
Genealogists interviewed by NBC News said the sample could contain too high a proportion of Nancy Guthrie's DNA.
"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," Colleen 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?" Fitzpatrick added.
Other genealogists told NBC News that mixed DNA samples can often take more time to find a match. CeCe Moore, the chief genetic genealogist at Parabon, a Virginia lab specializing in forensic genetic genealogy, said race and ancestry can also play a role.
"If the person of interest in this case has deep roots in the U.S. and is a white person, they could be identified in minutes or hours," Moore told NBC News.
"The vast majority of the people in the databases we have access to have primarily northwest European ancestry and deep roots in the United States," Moore added.
"If it's somebody who doesn't have connections to the U.S. in their tree in more recent generations, then it could take much longer," Moore continued.
Sam Barron ✉
Sam Barron has almost two decades of experience covering a wide range of topics including politics, crime and business.
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