Investigators are honing in on the man seen in chilling footage tampering with Nancy Guthrie's doorbell camera the night she disappeared, an ex-FBI agent has claimed.

Savannah Guthrie's 84-year-old mother was abducted from her $1 million Tucson, Arizona, home in the early hours of February 1. 

No suspects have been named and there have been no arrests in the four-month-long investigation.

Investigators previously released surveillance footage that showed a masked man at Nancy's doorstep on the night she disappeared.

The individual appeared armed and was observed tampering with a security camera mounted near the entrance.  

Former FBI agent Maureen O'Connell claimed on a recent episode of The Megyn Kelly Show that investigators are narrowing in on that suspect, which she believes will be the key to solving the case.

'I think they're getting close to the porch guy, and when they get the porch guy, the floodgates shall swing open,' O'Connell said.

She estimated that investigators are approximately 75 percent of the way there on nailing down the suspect and making an arrest. 

'I think they're close right now to pulling this case together, and that's what my sources are telling me. Things are happening,' O'Connell added.

The FBI recovered Nancy's doorbell camera footage days after she disappeared by accessing residual data stored on backend servers.

Pima County Sheriff Chris Nanos had previously said no footage was available because Nancy did not have a subscription to Google's video storage service, which typically keeps recorded clips in the cloud. 

The black-and-white video shows a masked figure wearing gloves tampering with her camera shortly before it was disconnected at 1.47am on February 1.

In her first interview since her mother's disappearance, Savannah told her colleague Hoda Kotb in March that the footage is 'absolutely terrifying.'

'I can’t imagine that is who she saw standing over her bed. I can’t,' Savannah said.

'I wake up every night in the middle of the night. And in the darkness, I imagine her terror. And it is unthinkable, but those thoughts demand to be thought.'

On Tuesday, Savannah made another emotional plea on the Today show, begging for help in the search for her missing mother.  

'I love you guys, and I love this place, and this is unusual and unprecedented to say the least to be sitting here, but you know, I don't have any comment on this story, and I'm not involved in our coverage,' she told her co-stars, visibly emotional.

'But I can't pretend I'm not here. So, since I am, I just want to take the opportunity to ask people to really to beg people to come forward - somebody knows something.'

The Guthrie family is offering a reward of up to $1 million for information leading to Nancy.

Earlier this week, it was revealed that a ransom note the family received back in February claimed that the senior had died.

Two notes were sent to Nancy Guthrie's family and local news outlets in the days after her January kidnapping. 

The first demanded millions of dollars in bitcoin in exchange for her release. The second claimed the she died, according to sources cited by CBS.

In the latter message, the suspected kidnappers reportedly insisted they never intended for Guthrie to die and offered an apology to her family