The latest development adds to the growing number of false leads and blunders in an investigation that appears to be no nearer catching Caroline's killer, despite two separate inquiries by the French authorities over the past 29 months.
Yesterday's disappointment involved a homeless man in his 30s who was arrested in Marseille on Wednesday after he was said to bear a resemblance to a photofit of the suspected killer reissued last month.
But the French police announced yesterday that a DNA sample from the man had proved a negative match and that he had been released.
He was arrested a week after it was revealed that detectives investigating 13-year-old Caroline's murder were examining possible links with the rape of a teenage girl in eastern France three years earlier. The girl told police that a photofit of the suspect in the Caroline investigation bore a resemblance to the man who had raped her at knife-point in Nancy in May 1993.
The rape victim described her attacker as a "caveman", with long dark hair covering his ears, a broad forehead, flat nose and bushy eyebrows.
Caroline was raped and suffocated with a pillow on 18 July 1996 in the room she was sharing with four schoolfriends at a youth hostel in Pleine Fougeres in Brittany while on a trip from Launceston College in Cornwall.
The possible link emerged after police investigating Caroline's murder issued a photofit of an unshaven, bushy-browed man with long, untidy hair. It was based on sightings of a man near the hostel.
In a separate development, French police are still investigating a claim that an Englishman resembled the artist's impression of the suspected killer. Pierre Rabin, an undertaker in Calais, told police that the picture is similar to a customer who called in at his funeral parlour in the town in 1995, a year before Caroline's death. He gave police a photocopy of the man's passport.
Despite this possible sighting, the French investigation appears to be making slow progress. Two days after the murder, the police arrested a man in connection with the killing. The investigating magistrate later declared the case closed, saying Patrice Pade, 41, had confessed.
But DNA testing proved him innocent too and the French authorities were later forced to pay damages of Fr10,000 (about pounds 1,000) for false imprisonment.
Over the next few months the murder hunt was dogged by a succession of blunders. DNA tests were ignored until too late because they were considered "too expensive", potentially vital witness statements were missed because they had not been translated into French, and door-to-door inquiries in and around Pleine Fougeres were barred for fear of "disturbing the local community".
After complaints by Caroline's parents the investigating magistrate was replaced, in August last year, by judge Renaud Van Ruymbeck. Since then more than 2,000 DNA tests have been done.
Police have also been searching for a French man who told tourists in the Republic of Ireland in July that he had fled his home country and could not return.
Despite the failure to catch the man who killed his daughter, Caroline's father, John Dickinson, 42, said yesterday: "I am sure it will be through one of these new leads that there will be a major breakthrough.
"I do not have any negative criticisms to make about the police any more, the new team are doing a sterling job and are really determined to catch Caroline's killer."