Guthrie is the 84-year-old mother of "Today" show co-host Savannah Guthrie.
He declined to answer another question about Mother's Day, which is Sunday.
Late last month, a private forensic lab in Florida sent a hair sample to the FBI for more advanced analysis.
Experts have told Fox News Digital the hair could be used for investigative or forensic genetic genealogy if it doesn’t match anyone known to have been in Guthrie’s home, potentially pointing a task force of county detectives and FBI agents toward a suspect.
Relatives and workers who had reason to be at Guthrie's home have previously given voluntary DNA samples, so the hair could point to a suspect if it doesn't match any of them.
"Building DNA profiles from hair or other forensic evidence does not necessarily take long," said Dr. David Mittelman, co-founder of Othram, a leading private forensics laboratory.
"In the 'Idaho Four' murders, for example, the DNA profile was developed within days. The challenge in forensic genetic genealogy is not simply generating a DNA profile, but generating a high-quality profile. Poor-quality or incomplete DNA profiles can make genetic genealogy difficult, ambiguous, or even impossible."
That's because an incomplete profile can lead researchers to miss potential familial connections that could help find a suspect.
"If you don't have a good profile, you may not see all the genetic relatives," he added. "It can be harder to resolve how people are related or not."
Nanos said previously that investigators believe Guthrie was taken from her home around 2:30 a.m. on Feb. 1.
A man in similar clothing was spotted about three weeks earlier approaching her door again.
He has not been publicly identified, but retired FBI profiler Jim Clemente told Fox News Digital this week that he believes the suspect made a number of mistakes that could help investigators identify him, if someone in his inner circle doesn't come forward first.
There is a combined reward of more than $1.2 million to solve the case.
To remain anonymous, contact Tucson's 88-Crime tip line at 520-882-7463.
The Guthrie family is urging anyone with information to dial 1-800-CALL-FBI.