Nancy Guthrie Case: Sheriff Issues Warning About Major Issue

Pima County Sheriff Chris Nanos is spearheading the local investigation into Nancy Guthrie's disappearance, not without some controversy. Nanos said he has 400 personnel working the case, which is now in its 22nd day.

In a new interview this weekend, Nanos discussed some of the DNA evidence collected from Guthrie's Tucson, Arizona home, which may present some "challenges" as authorities enter it through nationwide databases.

'Mixed' DNA making things harder

In an episode with "NBC Nightly News" that aired Saturday, Nanos revealed that the samples from the house are "mixed," meaning they contain DNA from more than one individual.

This makes it tougher to identify a potential database match.

"Our lab tells us that there are challenges with it," Nanos said. "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."

Progress made elsewhere?

Nanos also said he thinks police are making inroads on identifying articles of clothing worn by a potential suspect in surveillance footage from outside Guthrie's home.

"I think we're getting a little closer to identifying some of the other articles, not just that backpack. Like the shoes, the pants, the shirt or jacket," he explained.

It has already been revealed that the backpack the subject wore is a black black Ozark Trail Hiker backpack, sold exclusively at Walmart.

A message to the family

Nancy Guthrie, 84, was last seen at her house on the night of Saturday, Jan. 31. The following day, Sunday, Feb. 1, she was reported missing after failing to show up at a neighbor's house for a planned gathering.

Since then, there have been tens of thousands of reported tips, with the Pima County Sheriff's Department and FBI digging into any lead. Several ransom notes have also been sent to TMZ.

Nanos delivered a brief message to Nancy's family Saturday, which includes her daughter Savannah, longtime journalist and co-host of NBC's Today.

“We’re not quitting. We’ll find her," he promised.