The governor said the current investigators were "targeting the right suspects."

Mr Owens also said investigators were currently analysing "substantial new evidence" and that there was now "a reasonable belief that there was more than one person involved."

JonBenet Ramsey's parents, Jon and Patsy, reported their daughter missing on Boxing Day 1996.

Pat Ramsey: Found ransom note

Mrs Ramsay said kidnappers had left a ransom note demanding $118,000 for her return.

However, the six-year-old's body was discovered just hours later in the basement of the family home in Boulder.

She had been strangled and beaten to death. An autopsy revealed that she may have been sexually assaulted.

Suspicions rapidly fell on her wealthy parents, who resisted police attempts to interview them for months after the killing.

The Ramseys have consistently declared their innocence.

Within months of their daughter's death, the parents and their 10-year-old son Burke returned to Atlanta, Georgia, where they had once lived and where JonBenet is buried.

A Colorado grand jury investigated the case for 13 months.

But it completed its work on 14 October without finding sufficient evidence to charge anyone.

Alex Hunter: Parents are still not ruled out

Alex Hunter, Boulder's district attorney, said at the time that investigators had not yet ruled out the parents as suspects.

On Wednesday, Governor Owens had strong words for JonBenet's parents, telling them to return to Colorado and to "quit hiding behind their attorneys, quit hiding behind their PR firm."