Questions are being raised about the murder confession made by US teacher John Mark Karr as Thai authorities prepare to deport him.
The 41-year-old says he killed child beauty queen JonBenet Ramsay in 1996.
But there is widespread speculation Karr could have admitted to a notorious crime he did not commit, perhaps to draw attention to himself.
Crime author Carlton Smith said: “Occasionally you do have people make false confessions and that is something that the police need to be aware of and they need to take the track of saying to the confessor, ‘prove it to me that you did this’.”
JonBenet was found dead in the basement of her home in Boulder, Colorado.
She had been strangled and there was evidence of sexual assault.