Hopes were raised when investigators said they found DNA inside the Arizona home of Today show co-host Savannah Guthrie’s mother Nancy Guthrie, who vanished in the early hours of Feb. 1.

The DNA found inside Guthrie’s house, however, was “mixed,” complicating the search for the 84-year-old mother of three, Pima County Sheriff Chris Nanos told NBC News on Friday, Feb. 20.

“We listen to our lab, and our lab tells us that there’s challenges with it,” Nanos told NBC News, noting that it could take “weeks, months or maybe a year” to get results.

A mixed sample contains genetic material from more than one person, which makes it harder to identify, CeCe Moore, the chief genetic genealogist at Parabon Nanolabs, tells PEOPLE.

“A complex mixture is much more difficult to work with,” says Moore, who has helped law enforcement solve more than 300 cold cases using DNA and genetic genealogy.

“The more people you get in that DNA (sample), particularly unknown people’s DNA, the harder it is to just isolate one person’s out of that,” says Moore.

Sheriff in Nancy Guthrie Kidnapping Case Says Investigation Is ‘Still Growing’ as Search Enters Fourth Week

Moore is not part of the investigation, but has worked with the lab the Pima County Sheriff’s Office is using to identify the genetic material. “They’re very, very good at what they do,” she says. “So if they are struggling with it, that tells me it’s a very difficult sample.”

Based on what she has heard on the news about the evidence, she says she believes it’s “less likely to be a blood sample or something that is a really good source of DNA.”

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The good news, though, is the fact that DNA evidence was found in the first place.

“If I was the kidnapper, I would be extremely worried right now, particularly if I knew there was some kind of altercation, or I knew I touched things in there,” says Moore.

Speaking about the armed assailant who was caught on Nest camera surveillance video at Nancy’s front door, Moore says that person wore gloves and a mask to try to avoid leaving DNA behind.

But that is very difficult to do, she says. “It looked like he may have had a bite flashlight in his mouth,” she explains. “When you see him bending over toward the camera, I think it’s very possible saliva could have been left because of that.”

He could have easily transferred his saliva onto those gloves and then onto anything he touched, such as a doorknob, she says.