All three ransom notes sent to media outlets following the disappearance of Nancy Guthrie were fake, according to the FBI.
The 84-year-old mother of US breakfast show host Savannah Guthrie went missing on 1 February and has not been seen since.
Two notes were sent to the media in the immediate aftermath of her disappearance, while a recent third message claimed to know the kidnappers' identities.
But speaking to the Reuters news agency, a senior FBI official confirmed none of this correspondence is believed to be genuine.
The development could raise doubts on an initial theory that Ms Guthrie was abducted for ransom to begin with.
Savannah Guthrie, who hosts the Today show on NBC, had referred to the ransom demands in video messages, and said she was willing to pay.
Her mother, who had been in frail health with limited mobility, was last seen alive at her home in Tucson, Arizona on 31 January.
Footage later emerged that showed an armed man in a ski mask tampering with her doorbell camera shortly before her disappearance.
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DNA tests also concluded that blood found on the front porch was a match for Nancy Guthrie.
Celebrity news website TMZ had received the first note, which demanded cryptocurrency worth millions of dollars.
The FBI attempted to test its authenticity by depositing a small amount of cryptocurrency in the account mentioned in the note, but it was never claimed.
Savannah Guthrie has now returned to her role on the Today show and said a $1m (£760,000) reward remains on offer.
Last week, she told viewers that her family has remained in "agony" in the months since her mother's disappearance.
Media coverage of the case in the US has waned considerably in recent months, with Savannah Guthrie acknowledging her mother "may already be gone".
(c) Sky News 2026: Nancy Guthrie ransom notes were fake, FBI says
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