TUCSON, AZ — Testing on hair found at the Tucson, Arizona-area home of "Today" show host Savannah Guthrie's mother is complete and does not point to a suspect in the 84-year-old's abduction, Pima County Sheriff Chris Nanos told ABC News on Thursday.

"The hair was done ... and there was nothing," Nanos said in an interview.

That leaves a mixed sample of DNA retrieved from Nancy Guthrie's home as the only known piece of biological evidence, and one that has so far not been affirmatively linked to a suspect.

The sample is a mix of as many as four people, the sheriff revealed. It's not clear the technology even exists yet to untangle it, though the sheriff said multiple labs across the country are trying, including the FBI lab in Quantico, Virginia, and labs in Kansas, Florida, California and Arizona.

"My understanding is there are at least five, maybe six, labs across the country that are working on all of this," Nanos said. "We have some of the brightest minds in the nation, if not the world, working on this."

Investigators believe Guthrie was taken from her home in the early hours of Feb. 1 by a masked man captured on her doorbell camera. But six months later, Nanos is unable to say whether that masked man was working alone.

"I don't think anybody's here ready to say it's one guy, it's 10 guys," Nanos said. "Did he have help? Could have."

Nanos still believes the case is solvable, and he applauded Savannah Guthrie for keeping it in the spotlight through her Instagram posts, including one just this week.

"Somebody in our community, somebody out in this world knows something. Call us, tell us, give us that information. Somebody knows where Nancy's at. We need their help," the sheriff said.