reports.
Oliva, who is currently serving a 10-year sentence for possessing images of child abuse, sent Vail letters from his prison cell in Colorado in which he said he'd killed JonBenét.
In the upcoming interview, Dr Oz asks Vail if Oliva could be making it all up due to mental illness.
Vail concedes that "it's possible", before Grace prompts him to tell Dr Oz about Oliva's desire to eat JonBenét.
He says: "Yeah. I know it's some pretty heavy duty stuff, he's just talking about cannibalism."
Summarising, Grace says: "He said he wanted to eat JonBenét."
Vail then goes on to claim Oliva had broken into the University of Boulder Colorado to fulfil a horrific curiosity.
He said: "There was a skeleton in there and he wanted to taste what human bones would taste like.
"So he tried biting the skeleton and he told me how disappointed he was that it was covered with shellac, and he couldn't taste the bone."
The JonBenét Ramsey Case
JonBenét Ramsey was found dead on December 26, 1996 in the basement of the family home in Boulder, Colorado.
Her parents, John and Patsy, had a party the night before on December 25 and put their daughter to bed about 9pm.
Patsy woke up at 5am to find a three-paged ransom note on the stairs claiming JonBenét had been kidnapped.
She was found by her father in the basement and had been bludgeoned, strangled and hidden underneath a white blanket with a nylon cord around her neck, her wrists bound above her head and her mouth covered by duct tape.
JonBenét's parents and brother were formally cleared of any involvement in 2008 with DNA evidence.
Her brother Burker, who was nine at the time, was implicated in her death after a CBS documentary came out in 2016.
He has since publically denied it.
Oliva was obsessed with the child beauty queen and Vail suspected he had murdered her since he received a call from Oliva on the night her body was found saying he had "hurt a little girl".
JonBenét’s death made national headlines in the US in December 1996 when she was found dead in the basement of her family’s home in Boulder, Colorado.
Detectives believe she was murdered on Christmas Day.
Nobody has been charged with her killing.
The child beauty queen was bludgeoned, strangled and hidden underneath a white blanket with a nylon cord around her neck, her wrists bound above her head and her mouth covered by duct tape.
The family were immediately thought of as suspects by police, but JonBenét’s parents and brother were cleared in 2008 by DNA evidence.
In a recent letter, Oliva reportedly claimed: "I pleaded guilty to the murder of JonBenét as well as countless charges of assaults and sexual abuse against many children, there were various agreements made by me and the court which I signed many pages."
The letters have since been shown to Boulder Police.
Laurie Ogden, spokesperson for the local police, said: "The Boulder Police Department is aware of and has investigated Mr Olivas’ potential involvement in this case.
"We have passed the additional information [which was] provided on to investigators. We will not comment on any actions or the status of this investigation."
Netflix documentary casts new light on JonBenet Ramsey case
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