Guthries may be using coded language to communicate with mother's abductor

A former FBI agent said on Monday that she was "personally distraught" by the correspondence between Nancy Guthrie's daughter and her mother's abductor.

Bryanna Fox, an associate professor at the University of South Florida and a former FBI agent, told CNN's Jake Tapper during an interview on "The Lead" that the video Nancy's daughter Savannah Guthrie posted on Saturday had her concerned that she may have been communicating with the abductor using coded language.

"I was personally distraught. I was really worried, exactly what you said, that there was a lack of optimism," Fox told Tapper. "It just seemed like they weren't reaching out to their mother, and they were speaking to this ransomer. And I was really worried about what that could have meant from the last message that was sent ..."

On Monday, Savannah Guthrie posted a new video where she said the family still believes their mother is "out there." She also pleaded for the public's help in finding her mother and shared a detail that could help digital investigators locate her.

Fox said Savannah Guthrie's message also seemed to signal a change in the family's strategy.

"She's maybe nervous that either the ransom notes aren't, in fact, valid and legitimate and they were dealing with somebody that brought them no closer to finding their mother," Fox said. "So at this point, she may be just thinking, well, I'm going to invite the entire public, my viewership, everybody that cares about this case, as so many people do, to try to help solve it, and that could be by sharing that small detail that could lead investigators towards where her mother is at."