What to know about the investigation into Nancy Guthrie's disappearance and the search for clues

TUCSON, Ariz. — Law enforcement agents have been gathering more potential evidence as the search for ''Today'' show host Savannah Guthrie 's mother heads into its third week.

Nancy Guthrie, 84, was last seen at her Arizona home on Jan. 31 and was reported missing the following day. Authorities say her blood was found on the front porch. Purported ransom notes were sent to news outlets, but two deadlines for paying have passed.

Authorities have expressed concern about Nancy Guthrie's health because she needs vital daily medicine. She is said to have a pacemaker and have dealt with high blood pressure and heart issues, according to sheriff's dispatcher audio on broadcastify.com.

Here's what to know about her disappearance and the intense search to find her:

Video of masked man

The Federal Bureau of Investigation released surveillance videos of a masked person wearing a handgun holster outside Guthrie's front door in Tucson the night she vanished. A porch camera recorded video of a person with a backpack who was wearing a ski mask, long pants, jacket and gloves.

On Thursday, the FBI called the person a suspect. It described him as a man about 5 feet, 9 inches tall with a medium build. The agency said he was carrying a 25-liter ''Ozark Trail Hiker Pack'' backpack.

Studying DNA

Investigators collected DNA from Guthrie's property which doesn't belong to Guthrie or those in close contact with her, the Pima County Sheriff's Department said. Investigators are working to identify who it belongs to.

Evidence requiring forensic analysis is being sent to the same out-of-state lab that has been used since the beginning of the case, the department said.

Investigators found several gloves, the nearest about 2 miles (3.2 kilometers) from Guthrie's home, and submitted them for lab analysis, the sheriff's department said. It did not specify what type of gloves.

The sheriff stressed his department is working closely with the FBI.

The Pima County sheriff and the FBI announced phone numbers and a website to offer tips. Several hundred detectives and agents have been assigned to the case, the sheriff's department said.

The FBI said it has collected more than 13,000 tips since Feb. 1, the day Guthrie was reported missing. The sheriff's department, meanwhile, said it has taken at least 18,000 calls.

The sheriff's department has not said whether any tips have advanced the investigation.

Intensive searches

Late Friday night, law enforcement sealed off a road about 2 miles (3.2 kilometers) from Guthrie's home as part of their investigation. A parade of sheriff's and FBI vehicles, including forensics vehicles, passed through the roadblock.

On Tuesday, sheriff deputies detained a person for questioning during a traffic stop south of Tucson. Authorities didn't say what led them to stop the man but confirmed he was released.

The same day, deputies and FBI agents conducted a court-authorized search in Rio Rico, about an hour's drive south of the city.

Family pleas

Savannah Guthrie, her sister and her brother have shared on social media multiple video messages to their mother's purported captor.

The family's Instagram videos have shifted in tone from impassioned pleas to whoever may have their mom, saying they want to talk and are even willing to pay a ransom, to bleaker and more desperate requests for the public's help.

A quiet neighborhood

Nancy Guthrie lived alone in the upscale Catalina Foothills neighborhood, where houses are spaced far apart and set back from the street by long driveways, gates and dense desert vegetation.

Savannah Guthrie grew up in Tucson, graduated from the University of Arizona and once worked at a television station in the city, where her parents settled in the 1970s. She joined ''Today'' in 2011.