Clothes belonging to one of the victims, cigarette butts found on the scene and pieces of the murder weapon would be tested, the source told AFP, confirming a report from broadcaster RTL.

British-Iraqi tourist Saad al-Hilli, 50, his 47-year-old wife and his 74-year-old mother-in-law were found dead on September 5, 2012 in their car near the town of Chevaline in eastern France.

Each of them bore multiple gunshot wounds to the head.

One of the couple's two small daughters was badly wounded, while the second escaped unharmed by curling up under her mother's legs.

A local cyclist, 45-year-old Sylvain Mollier, was also shot dead.

France's national cold cases unit has been working on the murders since September 2022.

Prosecutors in Nanterre, the western Paris suburb home to the cold cases unit, confirmed that "new technical assessments were restarted in early 2024... to try and identify the perpetrator or perpetrators".

"We do not yet have their results," the prosecutors added.

Lawyer William Bourdon, who represents several plaintiffs in the case, told AFP his clients are clinging to hope the killer can be found.

Pieces from the butt of the vintage Luger pistol used in the killings -- a model issued by the Swiss army in the 1930s -- were found on the ground near the victims' BMW car.

But the weapon's owner has never been identified.

The recovered pieces are among those sent for DNA analysis.