Nancy Guthrie case: Former FBI agent analyzes mysterious abduction of Savannah Guthrie's mom

A motive remains unknown as the search intensifies for Nancy Guthrie, the mother of "Today" show host Savannah Guthrie, who investigators say appears to have been kidnapped from her Tucson, Arizona, home.

The 84-year-old was last seen Saturday night, and investigators believe she was abducted in her sleep early Sunday morning, the Pima County Sheriff's Department said.

Here's a closer look at the case with insight from ABC News contributor and former FBI agent Brad Garrett:

<h2>Possible motive</h2>

The sheriff's office said Thursday that investigators had not identified a suspect or a person of interest.

While the abduction could be random, according to Garrett, there are several possible motives.

"Is it personal to Nancy, somebody in her circle?" Garrett said. He called that unlikely, but a possibility.

The motive could be to target "her daughter, Savannah, who has this huge, international profile," Garrett said.

Garrett said it could also be mistaken identity.

"Houses have been broken into, people have been abducted and even killed, when the bad guys went in the wrong house," Garrett said.

And if the case is random, Garrett said, it's "much more difficult to solve."

<h2>Kidnap for ransom?</h2>

Another possible motive is a kidnap for ransom. The sheriff's department said on Tuesday it was reviewing possible ransom notes. ABC Tucson affiliate KGUN said it received one of the letters, which it forwarded to law enforcement. 

Savannah Guthrie and her siblings spoke directly to the potential kidnappers in a heart-wrenching Instagram video on Wednesday.

"We too have heard the reports about a ransom letter in the media," they said. "As a family, we are doing everything that we can. We are ready to talk. However, we live in a world where voices and images are easily manipulated. We need to know without a doubt that she is alive and that you have her. We want to hear from you and we are ready to listen. Please reach out to us."

Garrett said he assumes Savannah Guthrie coordinated the video with law enforcement because it "hit all the points I would've suggested to her to hit."

"'We want to speak to you,' Savannah is saying to the kidnappers. 'We want to know that our mother is alive and we want to talk to you about how to get her back' -- that's everything you would want to get out to the kidnappers in hopes that they then will turn around and contact the family," Garrett said.

In the video, Savannah Guthrie and her siblings addressed their mom as "mommy" and described her as a "kind, faithful, loyal, fiercely loving woman of goodness and light."

"She's funny, spunky and clever," they said. "She has grandchildren that adore her and crowd around her and cover her with kisses."

Garrett said the siblings "humanized their mother and talked in very kind, loving ways about her because you're trying to touch the heart, maybe, of somebody who kidnapped [her]."

"You just never know what switch it'll flip in people to, maybe, do the right thing," he said.

<h2>Potential evidence </h2>

The evidence left at Nancy Guthrie's home will be very important for investigators, Garrett noted. Authorities have not released specifics, but did say "we do in fact have a crime scene" and said "there were circumstances on scene that we believe are suspicious in nature."

Sheriff Chris Nanos said on Thursday that blood on the porch "came back to Nancy."

Authorities said they have Nancy Guthrie's phone, which Garrett said helps reveal her recent communications, and Garrett said investigators have certainly pored through footage from local traffic and surveillance cameras.

Sources told ABC News on Wednesday that the FBI is sending additional agents and experts to help reinforce efforts on the ground. Among those being sent is a supervisor who will run a task force with expertise in hostage negotiation and technology, sources said.

The FBI may bring expertise to the table like specialized technology to find and collect trace DNA, Garrett said.

The FBI experts may also use "3D laser technology, where you can create a 3D dimension of the house," Garrett said. Experts in blood spatter analysis can use that 3D replication to map out what happened at a crime scene and potentially determine the weapon used or the extent of an injury, he said.

<h2>'Extremely concerned' </h2>

As the search for Nancy Guthrie reaches the fifth day, Garrett said, "I am extremely concerned about her well-being."

Authorities said Nancy Guthrie suffers from some physical ailments and could die without access to her medication in 24 hours.

"If you combine the trauma and stress of being abducted, and if she got hurt at the scene ... and her not having medication, really puts her in the category of perishing," Garrett said.

Anyone with information is urged to call 911 or the Pima County Sheriff's Department at 520-351-4900.