By then the man was released after questioning, leaving it unclear Wednesday where the investigation stood into last week’s disappearance of Guthrie, the 84-year-old mother of “Today” show host Savannah Guthrie.

FBI agents fanned out across a neighborhood about a mile from Guthrie’s home on Wednesday morning, knocking on doors and searching through the dense desert terrain filled with cactus, bushes and boulders. Several hundred detectives and agents are now assigned to the investigation, which is expanding in the Tucson area, the Pima County Sheriff’s Department said.

A day earlier, authorities said they had stopped a man near the U.S.-Mexico border, just hours after the FBI released videos of a person wearing a gun holster, ski mask and backpack and approaching Nancy Guthrie’s home in Tucson. The man told media outlets early Wednesday that he was released after several hours and had nothing to do with Guthrie’s disappearance last week.

Authorities have not said what led them to stop the man Tuesday but confirmed he was released. The sheriff’s department said its deputies and FBI agents also searched a location in Rio Rico, a city south of Tucson where the man lives.

It was the latest twist in an investigation that has gripped the nation since Nancy Guthrie disappeared on Feb. 1. Until Tuesday, it seemed authorities were making little headway in determining what happened to her or finding who was responsible.

The black and white images released by the FBI showing a masked person trying to cover a doorbell camera on Guthrie’s porch marked the first significant break in the case. But the images did not show what happened to her or help determine whether she is still alive.

FBI Director Kash Patel said investigators spent days trying to find lost, corrupted or inaccessible images.

Even though the images do not show the person’s face, investigators are hopeful someone will know who was on the porch. More than 4,000 calls came into the Pima County sheriff’s tip line within the past 24 hours, the department said Wednesday afternoon.

Authorities have said for more than a week that they believe Nancy Guthrie was taken against her will. She was last seen at home Jan. 31 and reported missing the next day. DNA tests showed blood on her porch was hers, authorities said.

Savannah Guthrie posted the new surveillance images on social media and said the family believes their mother is still alive.

The longtime NBC host and her two siblings have indicated a willingness to pay a ransom.

It is not known whether ransom notes demanding money with deadlines that have already passed were authentic, and whether the family has had any contact with whoever took Guthrie.

TMZ reported it received a message Wednesday from someone claiming to know the kidnapper’s identity and that they unsuccessfully tried to reach Savannah Guthrie’s brother and sister. The person asked for bitcoin in exchange for the information, TMZ said. The FBI did not immediately respond to a message.

Authorities have said Nancy Guthrie takes several medications and there was concern from the start that she could die without them.

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Associated Press reporters Hallie Golden in Seattle, John Seewer in Toledo, Ohio, and Ed White in Detroit contributed to this report.