The FBI assessment pertains to the two ransom notes reported in early February, days after 84-year-old Nancy Guthrie went missing, and a third, more recent message from someone claiming to know the kidnappers' identities, the official said.
"None of the ransom notes are believed to be genuine," the FBI official told Reuters, speaking on condition of anonymity.
The disclosure seems to raise doubts about the premise that Nancy Guthrie was abducted for ransom.
A spokesperson for the Pima County Sheriff's Department, which is leading the overall investigation, declined to comment, citing its agreement to refer all inquiries regarding ransom notes to the FBI.
It has been four months since Nancy Guthrie vanished It has been four months since Nancy Guthrie, the mother of America's Today show co-host Savannah Guthrie, was reported missing.
Savannah Guthrie, 54, has referenced ransom demands in video messages she and her siblings have posted on social media.
The second note was reported by NBC News last week to have referred to Nancy Guthrie as having died. »