The BBC's Charles Eden reports

The man, said to be homelesss, French and in his early 40s, was arrested in Marseille and was described as "not being in possession of all his mental faculties".

He was reported to bear a resemblance to a photofit reissued last month of the suspected killer.

A photofit of a suspect issued in February

Genetic samples were taken from the man and sent to the National Police Laboratory. About 2,800 DNA tests have been already been carried out in the unsuccessful hunt for Caroline's killer.

Caroline was raped and smothered in a dormitory in a hostel in Pleine Fougeres, Brittany, in July 1996, while on a school trip from Launceston Community College, Cornwall.

The photofit picture which led to the brief arrest had been reissued last month after police linked Caroline's murder with the rape of a teenager in eastern France three years previously.

The student in the city of Nancy told police that a photofit of the suspect in the Caroline investigation looked like the man who raped her at knife-point in May 1993.

The rape victim attacked in Nancy described her attacker as a "caveman", with long dark hair covering his ears, a broad forehead, flat nose and bushy eyebrows.

He gave police a photocopy of the man's passport - including his full name, photograph and signature - which he took as proof of identity when the man went in to organise a funeral.

Caroline's father, John Dickinson, had said the suspect would be "ruled out or otherwise by DNA testing".

He said: "I am very pleased there seems to be a re-awareness throughout the whole of France with regard to the case."

He added that French police were "really determined" to find his daughter's killer.

French police are investigating a claim that an English man resembles the artist's impression of Caroline's suspected killer.