Details revealed in a chilling ransom note sent after Nancy Guthrie was kidnapped show “someone was there,” a retired FBI agent has claimed.

A pair of notes, reportedly sent from the same IP address, were sent to Guthrie’s family and news outlets days after she was abducted from her Tucson, Arizona, home on Feb. 1.

The first claimed that Guthrie, 84, was safe but the second said Guthrie – who had a heart condition – had died and been buried in nature, according to ABC News.

“The IP address match is one data point and it may or may not mean much depending on how sophisticated these people are,” Jason Pack, a retired FBI supervisory special agent with more than two decades of service, told The Post.

“What matters more is whether the style, tone, and language of the first two notes is consistent with each other and inconsistent with everything that came after. In my experience that’s where the real analytical work happens. Ransom communications have a fingerprint to them,” he added.

The first note reportedly included details about a broken floodlight in Guthrie’s yard and what she was wearing.

“Those aren’t things you read in a news report. Someone was there,” Pack said.

In the second note the authors apologized to Guthrie’s family and said she had died — but Pack does not believe it was some confession compelled by guilt.

“If the note is to be believed, notifying the family she was gone was the opening move in a new negotiation, not a moment of conscience,” he said. “But we’re taking the word of someone who abducted an 84 year old woman. That has to be factored into how much weight you put on anything they say.”