A grand juror, who was part of a panel which voted to indict the parents of six-year-old JonBenét Ramsey over her murder in 1996, has broken his silence to say he now knows who murdered the beauty pageant star.

Colorado's prosecutor disagreed with the jury's decision and chose not to proceed with the trial.

The juror, who risks prosecution for speaking out if he is identified, told US show 20/20 that the panel decided there was sufficient evidence to take JonBenét's parents to trial.

However, when asked if he thought there was enough evidence to convict John and Patsy Ramsey, he said no.

Asked by ABC's Amy Robach if he knew who killed the child, the juror replied: "I highly suspect, I do."

The juror does not say who he believes killed the little girl, whose body was found in the basement of the family home on Boxing Day morning in 1996. She had been bound, strangled and beaten to death and there was evidence of sexual assault.

DNA found on her body has never been matched, though investigators will be conducting new tests in 2017 when a new facility opens in Colorado, CNN reports.

JonBenét's parents and older brother Burke have all come under suspicion for the girl's murder. Handwriting expert Cina Wong says a rambling ransom note found at the home before JonBenét's body was found matches that of her mother, who died of ovarian cancer in 2006. The note had been written on a pad in the house.

JonBenét Ramsey was murdered at the age of six CBS

Both parents had been criticised for entering the child into "child beauty" pageants, relatively rare in Colorado but common in Patsy's home state of Georgia. Patsy had herself been a beauty queen.

Burke Ramsey, who was just nine when his little sister died, has also broken the silence to give an exclusive interview to "Dr Phil" on US TV. Many viewers found Burke's demeanour unusual as he smiled and laughed throughout the interview. However, Dr Phil says this may because he is awkward in social situations having been protected from the media for the past 20 years.

JonBenét's father was formally cleared of all involvement in her death by Boulder County District Attorney Mary Lacy in 2008. The investigation into JonBenét's murder remains open and active.