Cold case detectives believe DNA testing on a gun could hold the key to solving the murder of three Britons and a French cyclist in the Alps.
Engineer Saad al-Hilli, 50, his wife Iqbal, 47, and her mother Suhaila al-Allaf, 74, were shot in a layby close to Lake Annecy in 2012.
Passing cyclist Sylvain Mollier, 45, was also gunned down.
The al-Hillis' then seven-year-old daughter Zainab survived being shot in the shoulder and beaten around the head, while her sister Zeena, four, escaped by hiding in the back of the family's BMW.
Fragments of the murder weapon, a Luger P06, were found at the scene and French investigators in Paris have now ordered them to be unsealed so they can be tested with breakthrough technology. An investigating source said: “It is hoped that new examinations will uncover DNA traces.
“If yes, then they will be sent for comparison with a national genetic fingerprint file which lists more than a million fingerprints, to see if there is a match.”
The clothes Sylvain and Zainab were wearing at the time of the massacre on September 5, 2012 will also be examined along with 10 cigarette butts found in the area.
But the gun parts carry the most hope of a breakthrough as they are guaranteed to have been in direct contact with the killer.
Most of the vintage, Swiss army-issue, semi-automatic pistol was removed from the scene, but small pieces of the grip plates were found near the family's BMW.
DNA can be obtained from even a single fingerprint and analysis has improved significantly since the investigation was launched, the source said.
Iraq-born Saad al-Hilli, from Surrey, was on holiday with his family at the time of the tragedy, in which 25 shots are believed to have been fired.
The case has since baffled detectives with investigators struggling to find a motive for the family being targeted.
In January, a cold case dating back to 2008 was solved in France thanks to new DNA testing.
The body of jogger Caroline Marcel, 45, was found half-submerged in the river Loiret in Olivet.
New methods matched DNA found on her corpse with that held in the national database, leading to the arrest of a known sex offender.