Child killer or delusional lunatic - did this man really kill JonBenet?

John Mark Karr has confessed - but the facts don't match. Only DNA will reveal if he is telling the truth

The thin, nervous schoolteacher who confessed last week to one of America's most notorious unsolved child murder cases - the killing of six-year-old beauty pageant queen JonBenet Ramsey - will be escorted back to the US from Thailand today to face charges of homicide, kidnapping and sexual assault.

Whether John Mark Karr really is the man who broke into the Ramseys' home in Boulder, Colorado, the day after Christmas 1996 and strangled the little girl with a garrotte made from nylon and a broken paintbrush remains in considerable doubt, however.

An account of his initial confession to Thai police is inconsistent with key facts of the case. Mr Karr's ex-wife, Lara, who says she loathes him and has no reason to cover up for him, claims he was with her in Alabama at the time of the murder. Investigators are yet to provide a single piece of evidence that Mr Karr ever set foot in Colorado - in December 1996, or at any other time.

Perhaps most tellingly, Boulder County's chief prosecutor has held back from bragging about what, ostensibly, is a breakthrough arrest in the biggest case her office has ever handled. "Do not jump to conclusions, do not rush to judgement, do not speculate," District Attorney Mary Lacy admonished reporters the day after Mr Karr's arrest. She acknowledged that suspects are sometimes arrested before the investigation into them is complete, prompting several legal experts and newspaper columnists to suspect she had little or no case against Mr Karr at all.

Craig Silverman, a former prosecutor from nearby Denver, called Mr Karr's televised confession to reporters in Bangkok "nonsensical and delusional". Bill Johnson, a columnist with the Rocky Mountain News, wrote yesterday: "John Mark Karr as much killed JonBenet Ramsey as Mickey Mouse did... If you haven't noticed, the guy's a lunatic."

What we do know about Mr Karr is that he is obsessed with the JonBenet case and steeped in its every detail. In an email correspondence he struck up a few years ago with a Boulder journalism professor with an abiding interest in the case, he poured forth expressions of love for the girl and even forwarded a poem he had written. "JonBenet, my love, my life," it read. "I love you and shall forever love you. I pray that you can hear my voice calling out to you from my darkness - this darkness that now separates us."

Mr Karr's interest in children generally is open to question. Both his wives were teenagers when he married the them, the first just 13. And he was arrested in California five years ago for possession of child pornography - a charge that ended his second marriage. It also cost him his teaching licence and sent him on a journey to different short-term teaching jobs around the world.

What we don't know is how - if he really was the killer - he came to know about the Ramsey family in the first place, how he lured JonBenet into the basement of their large house, beat and killed her and made his getaway entirely unnoticed.

The circumstances of the murder remain shrouded in mystery, in part because the crime scene was compromised from the very start. JonBenet's parents reported her as missing and invited several friends and family members to the house. Her father, John Ramsey, later recovered the body from the basement and carried it upstairs. The Ramseys also found what appeared to be a ransom note demanding $118,000 for JonBenet's safe return.

The ransom almost exactly matched the Christmas bonus John Ramsey had just received from his computer consulting firm, leading investigators to suspect for a long time that the parents themselves were responsible for the murder. The handwriting on the note was a close enough match to Patsy Ramsey, JonBenet's mother, to keep her under a cloud of suspicion right up to the time of her death from ovarian cancer in June this year.

One intriguing clue in the ransom note has now been linked, if tentatively, to Mr Karr. Investigators have spent 10 years puzzling over the sign-off line "Victory! S.B.T.C." Now one of Mr Karr's old high-school yearbooks has surfaced, in which he wrote a message to a classmate that read: "Deep in the future, I shall be the conqueror and live in multiple peace." The words "shall be the conqueror" - acronym S.B.T.C. - are written in capital letters.

Legal experts agree there is only one way to establish whether or not Mr Karr is the killer, and that is to take a DNA sample and compare it with the male DNA found under JonBenet's fingernails and on a spot of blood found on her underpants.

Mr Karr underwent a DNA swab in Thailand on Friday, and is expected to be tested again when he arrives in the US. "That's going to be the key," former prosecutor and law professor Karen Steinhauser told the Rocky Mountain News. "If that DNA doesn't match, they won't be able to file this case no matter how big a confession they have."