The bones were discovered on the French Riviera sea bed, about six meters (19 feet) below the surface, by divers, and have been in the water for at least a decade, investigators said.
DNA tests on one, from an upper arm, revealed it belonged to Stephane Hirson, 17, of Paris, who disappeared in 1994. The others, including a male's thigh bone, a female's upper arm bone, a skull and part of a jaw, remain unidentified, the British newspaper The Guardian reported Thursday.
Detectives discovered the faded inscription "death to pedophiles" on the skull, which investigators say belonged to a male under the age of 50.
"We are confronted with a series of enigmas. There are a thousand questions in this case. Why, for example, a single bone for each individual and not other parts of the skeleton?" said Georges Gutierrez, Grasse, France, public prosecutor Wednesday, as he announced the opening of the inquiry.