Guthrie, the mother ofTodayco-host Savannah Guthrie, disappeared from her home in Tucson, Arizona, on 1 February. A ransom demand of $6 million (£4.7 million) was subsequently issued, with a deadline of 9 February, according to US media reports, focusing attention on how investigators and the family handle any contact with the alleged kidnappers.

Dan Donovan, founder and managing partner of US security consultancy Stratoscope Holdings, saidproof of life was a basic requirementin kidnap-for-ransom cases.

'Ransom is often not paid without proof of life because paying without verification risks funding a crime with no chance of recovery,' he toldRadarOnline. Proof of life, he added, both confirms the victim's status and demonstrates that the abductors retain control.

Retired FBI agent Scott Curtis, who has been commenting on the case in US media, echoed that view and said he believed Guthrie's family had not yet received such evidence.

'I believe they haven't received proof of life,' he said. 'You're not going to make a ransom payment unless you have proof of life.'

Curtis said he had urged caution for the family, which includes Savannah Guthrie, her sister Annie and brother Camron, about moving forward without confirmation of Nancy Guthrie's condition.

US broadcasters have reported that the FBI is running a 24-hour command post as the search enters its fourth week. Federal authorities have not publicly commented on any ransom demand or on whether there has been direct contact with the kidnappers.

Curtis said advances in artificial intelligence were making it more difficult for families and investigators to rely on images alone.

'There still could be some doubt in that proof of life, especially in this AI-generated world we're living in now,' he said, suggesting that any verification would need to be robust.

He argued that credible proof of life in the Guthrie case would likely require a video with audio, a definitive date stamp and details that would be hard to fabricate digitally.

Source: International Business Times UK