Dr Yves Godard disappeared earlier this month with his wife and two children after hiring a yacht in the Brittany port of St Malo. He is said to bear a resemblance to the photofit of Caroline's killer.
Caroline, 13, from Launceston, Cornwall, was raped and suffocated in a Brittany hostel during a school trip in July, 1996.
The French authorities issued an international arrest warrant for Dr Godard on Monday after investigators found blood in his home in Normandy. A manslaughter investigation was launched.
The prosecutor's office in Rennes confirmed that DNA tests will take place. But an official stressed that no link had been established between the two cases. The test was routine.
Godard is said to have hired a yacht in St Malo on 1 September. Police found its liferaft adrift off Roscoff but believe he may have staged a disappearance. A customs officer boarded the yacht on 2 September but saw only one child on board. Godard told him that his wife Marie, 40, and the second child were below deck.