TUCSON, Ariz. — Investigators couldn't obtain a DNA profile from a hair sample recovered from within Nancy Guthrie’s home, Pima County Sheriff Chris Nanos told Fox News Digital in a new interview Thursday, as the case nears the six-month mark.

"Yes, there was a hair. We had it and thought, 'Okay, well, we'll do the DNA first,' right? You're going to do DNA before something else," he explained.

Working with the FBI, investigators sent the sample to a California laboratory for additional DNA testing.

"It came back...there's no DNA," Nanos said. "But does that mean the hair isn't that of the suspect? We won't know that till we have the suspect's hair. You don't just destroy it."

Investigators have preserved the sample and it still may be of use later, he added.

"There's other things that hair may prove valuable for, but right now it was just about, 'Is there any DNA there?' And the answer was no," the sheriff said. "That was just a matter of weeks ago."

Guthrie is the 84-year-old mother of "Today" co-host Savannah Guthrie. She will have been missing for six months on Saturday.

Nanos indicated that the hair was only one part of the broader DNA work underway, though he did not specify how many other samples are being tested.

DNA testing remains a priority in the case, and Nanos said investigators continue working with multiple crime labs to analyze evidence collected from the scene.

"Anything we can grasp onto with DNA is a part of this investigation," he said.

That includes investigative genetic genealogy research, which is used to generate leads from a family tree. He noted rapid advances in DNA technology.

"That's really where some of my optimism is, that I just know that we're gonna get this thing resolved," Nanos said.

Meanwhile, there is a combined reward of more than $1.2 million that remains unclaimed.

"We believe, just as the family does, just as Savannah does, somebody knows something. We need that person to call us."

At least one suspect was recorded by Guthrie's Nest doorbell camera. According to the FBI, he is between 5 feet, 9 inches and 5 feet, 10 inches tall with a medium build. He was wearing a mask, long sleeves and gloves, and the backpack he carried has been identified as a black Ozark Trail brand bag.

The family is urging anyone with information to dial 1-800-CALL-FBI.

An anonymous reward can be claimed by calling 520-88-CRIME with information that leads to an arrest.