Why the Nancy Guthrie investigation is facing “mixed” DNA complications

TUCSON, Ariz. – Three weeks after Nancy Guthrie’s disappearance, DNA samples are creating challenges for investigators. Forensic scientists are having trouble isolating DNA recovered from Guthrie’s home here in Tucson.

The Pima County Sheriff told NBC News the samples are “mixed”—meaning they contain DNA from multiple people—making it harder to run through national databases. Experts say the issue could take months to resolve and could pose a problem if an arrest is made and the case goes to court.

What we know:

Investigators are still working to identify a suspect. They are looking for a man between 5 feet, 9 inches and 5 feet, 10 inches tall who was seen on surveillance video taken from Guthrie’s front porch. 

The sheriff’s department continues to examine surveillance footage from neighbors.

What they’re saying:

Those same neighbors have been bringing flowers, candles, and other mementos to a memorial outside of Guthrie’s home.

“We were neighbors for years. That’s the thing. In this neighborhood, we’re all kind of spread apart,” one neighbor said. “And she was living on her own… we’re all very much to ourselves and respectful to everyone around the neighborhood. But we all care about each other. And when something like this happens, we all pull together.”

As the investigation enters its 22nd day, many people are getting anxious, with some volunteers even going so far as to search for Guthrie themselves. However, the sheriff’s office says the community needs to leave the investigating to the professionals.

The reward has climbed to more than $200,000 in hopes it could compel someone to come forward.