It all began last February, when an amateur diver came across a skull and other bones, while searching for sea urchins off the Cap d'Antibes.
French police opened a murder inquiry and the bones apparently belong to at least four people, two men and two women.
Among the bones is the skull of a 50 year old male with the words "death to paedophiles" written in indelible ink and a drawing of a target sign.
In November, DNA testing indicated that the remains of 17 year-old Stephane Hirson were among the bones.
Hirson was a psychologically disturbed teenager who disappeared from his home near Paris in 1994.
But on Monday, the prosecutor's office in Grasse, which is leading the investigation, said a new DNA test had disproved that.
"There are a thousand questions in this case" said prosecutor Georges Gutierrez, "why did we only find one single bone per person?"
One femur, two humeruses, and one skull, each belonging to a different person, are the only evidence in the deepening mystery.