Patrice Pade, a 39-year-old drifter, confessed to killing Caroline Dickinson, 13, at a youth hostel in Pleine-Fougeres near Mont St Michel three weeks ago. But the examining magistrate in charge of the case confirmed yesterday that genetic material taken from Caroline's body did not appear to correspond with that taken from Mr Pade.
John and Sue Dickinson, Caroline's parents, called for "redoubled" efforts to track down the killer as the small town of Launceston, in Cornwall, where the teenager went to school, expressed horror at the sudden twist in events.
Mr and Mrs Dickinson said in a statement that their lives had been changed forever when their daughter had been killed and that it had been "a small consolation" when someone was apprehended for the crime.
"Now it seems we have been denied even this. We hope that the authorities will redouble their efforts to catch the culprit. Then the man who robbed Caroline of her future and us of a lovely daughter will not to be free to commit such a crime again."
Caroline was with a party from Launceston College when she was found raped and smothered last month on her mattress in the room that she shared with four friends.
Mr Pade was detained by French police using a portrait drawn from descriptions given by villagers. The area magistrate confirmed he had confessed to raping and murdering Caroline.
The suspect had twice been sentenced by French courts, the first time in May 1984 to three years in jail and two suspended sentences for indecent assault on a teenager. In 1993, he was sentenced for a public decency offence and was freed a year later.
Yesterday, court officials in France declined to comment but Mr Pade was not released from custody. A British embassy spokesman would not speculate on what the development might mean. Confirmation that the DNA tests did not appear to match has cast doubt on Mr Pade's confession, or suggests he had an accomplice.
Ronald Frankel, Britain's regional consul for the St Malo area, said the gendarmerie must have other lines of inquiry to pursue. "I don't think for one moment that whilst awaiting the results of these tests that they just sat back and left it like that."
Michael Valentine, Caroline's grandfather, said he was shocked. "We have just this minute heard it on the radio. It is bad news as far as I am concerned, it was just beginning to die down. It's terrible for the parents, terrible for everybody."
The Rev Tim Newcombe, the Launceston vicar who conducted Caroline's funeral service, said: "A tragedy which seemed to have a resolution now no longer has one. I have little doubt my views will be shared by most people in the community."Reuse content