A rare pistol of the same type used to brutally gun down a British family on holiday in the French Alps 14 years ago has been found at the bottom of a nearby lake.

Saad Al–Hilli, 50, an Iraq–born satellite engineer from Surrey, was shot dead at the wheel of his BMW on a remote mountain road near Lake Annecy in 2012.

His wife Iqbal, 47, her mother Suhaila, 74, and local cyclist Sylvain Mollier, 45, were also killed in a hail of bullets during the incident, which sent shockwaves throughout Europe.

Hand–grip fragments of a rare Luger PO6/29, Parabellum 7.65, were found at the scene, leading forensics experts to conclude that it was the weapon used.

Now, police divers have found the same kind of Swiss Army sidearm at the bottom of Lake Annecy, which at its deepest is 82meters (269ft).

An investigating source said: 'It was found in the water last week.

'The gun was immediately salvaged, and rushed away for forensic analysis.

'The time it has spent in the water will clearly make analysis extremely complex, but the priority is to work out if it was the one used in the quadruple murder.'

The killer fired 21 bullets in under two minutes, hitting his victims with 17 of them.

The Al–Hilli's seven-year-old daughter, Zainab Al–Hilli, was shot in the shoulder and beaten around the head with the gun, while her sister, Zeena Al–Halli, four, escaped by hiding in the back of the family's BMW car.

Detectives discovered the murder weapon was the kind of Luger issued to Swiss soldiers between 1909 and 1947, after being manufactured in either Switzerland or Germany.

Sabine Khéris, a magistrate who specialises in cold cases, later narrowed the scope of the inquiry by determining that the gun was built in 1935, when only 940 such Lugers were manufactured.

Ms Khéris said the killer was likely to have been 'methodical and calm', and had undoubtedly received 'shoot to kill' training, after performing 'double taps' on his victims.

A 'double tap' involves a shooter hitting a victim with a bullet, and then using another one to confirm a kill.

While DNA was once thought to be completely washed away in deep water, advancements in forensic technology mean profiles can sometimes be recovered.

Additionally, the gun will have a serial number which could help investigators track down its precise history, potentially up to the point it came into the hands of the murderer.

Experts working for France's cold case unit in the Paris suburb of Nanterre will re–test the original gun fragments from the scene of the crime, and compare them with the newly discovered pistol.

The Al–Hillis, of Claygate, Surrey, originally came from Iraq, with one theory being their links to the regime of former dictator Saddam Hussein may have been a reason for their murders.

There were also claims Mr Al–Hilli was involved in a dispute over a family inheritance, but this has been discounted because of a total lack of evidence.

Other theories include the main target having been Mr Mollier, the French cyclist, meaning that the Al–Hillis ended up as collateral damage.

Botched probes by French police have meant one suspect - feared to be a tourist-hating former Swiss soldier in his 50s - has so far avoided capture.

A theory previously emerged over the identity of the assailant, pointing towards a mystery 'camper' who pitched a tent near the mass shooting of the Brit family and by the scene of another random tourist murder, where a rare Swiss gun was also used.

An alleged Danish national was staying at a campsite on a rented pitch in the campsite of Saint-Jorioz, where the Al-Hilli family had set up their caravan from September 1, 2012.

Arriving on September 3, the 'Dane' - whose identity cannot be confirmed - left on September 5, the day of the Chevaline massacre.

French investigators claimed they had traced the same individual to a campsite less than six miles from the murder scene of another tourist Xavier Baligant, a year earlier. The site is about 300 miles north of where the Brit family was killed.

The 29-year-old was shot four times at a rest area near Nancy while he was heading home to Belgium following a camping trip.

He had stopped for a 'pee break' on the night of July 18 to 19, 2011, when his killer sneaked up and assassinated him.

His two sons Jordan and Dylan, then aged seven and five, were sleeping in his car when their father was slaughtered. They escaped unharmed.

Mr Baligant's murder - which appeared to be more like an execution - took place on a rural stretch of road on the A31, just a few miles from the campsite of the 'Dane'.

His killer fired five bullets, the first from about 50ft away and the last at point-blank range in the face.

It's thought the murderer was armed with a Schmidt-Rubin K31 rifle.

Baffled French detectives claimed the mystery camper was staying nearby on the night of the killings, reports French paper Le Parisien.

This man was therefore present at two murders, a year apart - where rare Swiss weapons were used.

However, it is not clear whether the 'camper' had booked under his own name or whether false details had been provided.

Prosecutors previously admitted a forensics officer accidentally contaminated key evidence with his own DNA, and that the area around the crime scene was inexplicably reopened to the public just 48 hours after the massacre.

The case has been plagued by speculation over possible motives, ranging from Mr Al-Hilli's high-security work in the satellite industry to family disputes over inheritance.

The local father-of-three was reportedly shot first and last, with more bullets than anyone else.

Former Surrey detective Mark Preston, who worked on the case, previously told a Channel 4 documentary that the Al-Hilli family may have been innocent bystanders caught in the crossfire of a targeted hit on Mollier.