The mother of US TV host Savannah Guthrie is believed to be alive after police allege she was kidnapped from her home in Tucson, Arizona, over the weekend.

On Wednesday, a ransom note was sent to news outlet TMZ demanding millions of dollars in Bitcoin. On Thursday, Pima County Sheriff Chris Nanos confirmed the department had received more than one ransom note and said investigators were taking them seriously.

“It’s like any piece of evidence,” Nanos told CBS News.

“You give it to us, you give us a lead, we’re going to look at every aspect of that lead.”

Authorities have said they believe that Nancy Guthrie is still alive.

“We have nothing else to go on but the belief that she is here,” Nanos told NBC.

“She’s present. She’s alive, and we want to save her.”

Nancy was last seen alive on Saturday (US time) and was reported missing the following day by family members after she failed to attend church.

Adding to the urgency of the investigation is the fact that Nancy takes daily medication to survive.

Despite speculation online, the sheriff’s department has confirmed there is no suspect in the case, including claims her son-in-law, Tommaso Cioni, may be involved.

“We have not identified a suspect or person of interest in this case. Detectives continue to speak with anyone who may have had contact with Mrs Guthrie. We are also awaiting additional forensic results,” the department said in a statement to TMZ.

Cioni became a focus of public speculation after police searched his vehicle.

Former Navy SEAL and FBI special agent Jonathan T. Gilliam told Sunrise on Thursday that such scrutiny is common, particularly when a person was the last known individual to see the victim alive, but it does not indicate police believe he was involved.

“I think in any case, the last people who had something to do with the victim are going to be investigated in some way, shape or form,” Gilliam said.

“And I do believe, if I’m remembering correctly, he’s the one who dropped her off and was the last person to see her.”

Jeff Wenninger, a former LAPD Lieutenant, told Sunrise that in his experience, only about 5 per cent of abductions include a ransom demand.

A desperate search for Nancy Guthrie, the mum of US TV host Savannah, has entered its fourth day and police are yet to uncover a break in the case of her suspected abduction.

(Source: 7NEWS)

A desperate search for Nancy Guthrie, the mum of US TV host Savannah, has entered its fourth day and police are yet to uncover a break in the case of her suspected abduction.

“Generally speaking, when you have an abduction, it’s some type of an incident regarding a domestic dispute or the commission of another crime like robbery or sexual assault,” he said.

Wenninger says statistically, the person responsible is likely someone Nancy knew.

He said the ransom notes that have been received will need to be closely examined to ensure their authenticity.

“What you’d be really looking at here is something that would determine that the person who sent this is sending something authentic in regards to they know something that only the person abducted would know,” Wenninger explained.

Investigators have confirmed the video camera at Nancy’s front door was removed, but Gilliam cautioned this does not necessarily point to a highly sophisticated crime.

Gilliam said footage from the incident, or at least of the person who removed the camera, could be stored in the cloud. However, he noted many users do not sign up for that service.

“Most of these home security cameras work on a cloud. There’s not anything being recorded in the camera itself,” he explained.

“So if somebody took that camera thinking that they were going to hide something, then they’re obviously not that sophisticated.”

However, Gilliam said the removal of the camera does suggest prior knowledge of the home, with elements of the case pointing to a targeted attack rather than a random crime.

“Statistically, this type of an abduction or a killing made to look like an abduction that has no robbery and is within a victim’s home where it appears that she’s been watched, that is typically a family member or a close acquaintance, or somebody that lives close by that has watched her,” he said.

Police continue to analyse all available evidence as the search for Nancy continues.