Authorities confirm the DNA belongs to Nancy Guthrie, 84, who was last seen on Jan. 31 at her home in Arizona

A local sheriff in Arizona tells PEOPLE that investigators discovered “biological DNA” evidence at Nancy Guthrie’s home after declaring the residence a “crime scene” during the search for the missing mother of Today show host Savannah Guthrie.

Law enforcement announced on Tuesday, Feb. 3, that the DNA evidence belongs to Nancy, but did not specify its nature.

Nancy, 84, was last seen around 9:30 p.m. on Jan. 31 at her home in Catalina Foothills, north of Tucson, Ariz., and investigators believe she was possibly kidnapped in the middle of the night, according to the Pima County Sheriff’s Department.

Savannah Guthrie and mother Nancy Guthrie.savannahguthrie/Instagram

Her disappearance was first reported on the morning of Sunday, Feb. 1, after a friend from her church noticed she was not at service and called one of her adult children. They then went to Nancy’s home to check on her, and “did some searching and realized, ‘We need some help,’ and they called 911,” Sheriff Chris Nanos previously said.

At a press conference, the sheriff announced that investigators believe a crime occurred, describing the case as more of a “crime scene” than a “search mission.” He previously called the scene “concerning” and said homicide detectives were working the case.

While Nanos has not specified what exactly led investigators to believe a crime had occurred, he told PEOPLE on Monday, Feb. 2 that in addition to utilizing a search and rescue team and reviewing surveillance footage, investigators “have taken what we believe is biological DNA-type evidence and we are submitting it to our labs.”

Savannah Guthrie and mother Nancy Guthrie.Savannah Guthrie/Instagram

The sheriff also told PEOPLE on Monday that Nancy’s “physical mobility was quite limited for a variety of reasons,” and that it is highly unlikely that she wandered off, despite her mental acuity.

“She is really just as sharp as a tack,” Nanos said. “And that too is concerning that here you have this lady who’s got all her wits about her, she knows what’s going on. So yeah, somebody came into that home, and I believe took her out there without her permission. It was against her will.”

According to the sheriff, Nancy also depends on medication that could become life-threatening if she goes without it for more than 24 hours.

The PCSD is now offering a reward of up to $2,500 for information related to Nancy’s disappearance. Officials are appealing to the public for “any video or photograph information” from the scene near her home.

Missing-person poster for Nancy Guthrie.Pima County Sheriff’s Department

Savannah, 54, remains in Arizona with her family as the investigation continues. In a message shared to Instagram Monday night, she urged her followers to pray for her mother’s safe return.  Nanos has said her family has been cooperative.

The PCSD describes Nancy as an 84-year-old female with brown hair and blue eyes. She is 5 feet 5 inches tall and weighs about 150 lbs.

People are encouraged to call 88-CRIME or 520-882-7463. All calls remain anonymous. They can also use the mobile app P3TIPS or visit 88crime.org.