A camera found on the roof of Nancy Guthrie's home could prove to be a crucial clue, a security expert has said.
The FBI and local police have been working in tandem to track down the missing 84-year-old since she vanished on 1 February.
Officials released footage of an 'armed' potential suspect on Tuesday (10 October), who was seen appearing to tamper with her doorbell camera on the morning of her disappearance.
Nancy is the mother of Today show host Savannah Guthrie and a ransom note left at the scene said the 84-year-old's release depended on a Bitcoin exchange worth $6 million.
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President Donald Trump has urged Americans 'with any knowledge of the suspect to please call the FBI', White House press secretary Karoline Leavitt said.
The individual seen in the video was sporting a mask, glove and a backpack.
Take a look at the footage here:
It is hoped this footage could lead to a crucial breakthrough in the kidnapping case which has stunned the US.
However, a security specialist reckons that another recording device set up outside Nancy's home in Tucson, Arizona, could also hold 'one of the most important clues'.
After police swooped on the property in wake of her disappearance, dozens of cops were seen descending on the pad - and one agent headed up to the roof.
Officials were seen removing what is believed to be a wired camera, which may have been found thanks to a tip from Nancy's neighbour, Laura Coates.
Coates told CNN that she had encouraged a detective to 'check out' the roof after noticing that it looked unusually clean and as though it had recently been recoated.
According to Dan Donovan, the founder of security and risk management firm Stratoscope Holdings, the camera found on the roof is 'not a throwaway detail'.
Speaking to Us Magazine, he explained: "It’s potentially one of the most important clues.
"A camera on the roof suggests surveillance, planning and situational awareness. That’s not the behaviour of someone improvising."
Sharing his theory, Donovan added: "It could mean they were watching entry points, watching police response patterns or monitoring the home to see who comes and goes."
He suggested that if it emerges that the ransom note and the wired camera were both left behind by those responsible for Nancy's disappearance, this 'reinforces something critical'.
"This may not be an emotional crime - it may be operational," Donovan went on. "And operational criminals tend to follow through when they feel control slipping."
Nancy's daughter Savannah has made numerous public appeals in wake of her mother's kidnapping alongside her older siblings Annie, 56, and Camron, 61.
The TV star shared the footage of the masked assailant released by the FBI on Tuesday to her social media pages, alongside the caption: "Someone out there recognises this person.
"We believe she is still alive. Bring her home."
The FBI has put up a $50,000 (£36,500) reward for information leading to Nancy's safe return.
Olivia Burke