A longtime friend of the Ramsey family believes JonBenet was killed by her brother Burke.

The mystery of who killed child beauty queen JonBenet Ramsey in 1996 has only intensified in the wake of new and upcoming televised investigations.

JonBenet was found bludgeoned and bloody at the bottom of her family’s basement after being reported missing.

The latest theory behind who was responsible for her murder has emerged from an interview given by a Ramsey family friend of more than 10 years.

Judith Phillips told The Sun she believes the six-year-old was killed by older brother Burke after an disagreement went violently wrong.

“I agree with the theory Burke killed JonBenet but I don’t think he meant to do it," she said.

"I think Patsy did everything in her power to protect her living child. I think she wrote the ransom note whilst John staged the scene in the basement."

"After calling the police Patsy began inviting friends over to the house and in the commotion John went missing for an hour and half. It is my opinion he was disposing of evidence.”

It was reported Phillips first became friendly with the Ramseys when they were neighbours in Atlanta, Georgia. The two families were said to have reconnected once more when they moved to Boulder, Colorado.

Listen: Why Australia watched The Case of JonBenet Ramsey. (Post continues after audio.)

The 64-year-old said the birth of JonBenet possibly triggered the beginnings of a long-held jealousy within the boy.

“When Burke was born he was the absolute apple of Patsy’s eye. Then along came this little girl who stole all the attention. He could well have been very jealous," she said.

Phillips also commented on the unusually long ransom note found by investigators.

“A phrase used, ‘And hence’, leaped out at me. I had received a Christmas newsletter from the family and the phrase was used in that too. It seemed like not something people generally say," she said.

The theory it was Burke who killed JonBenet was suggested by a former investigator in the CBS documentary series: The Case Of: JonBenet Ramsey.

The investigator theorised the two may have brawled over a bowl of pineapple.

A lawyer for the Ramsey family has announced into his intention to sue CBS for the documentary.