Police detained the man on Wednesday as part of a new investigation into the killings of Saad al Hilli, 50; his wife Iqbal, 47, and mother-in-law Suhaila al Allaf, 74, on a remote road near Annecy on 5 September 2012.

In a statement, the Annecy prosecutor said: "No charges have been brought against the person who was questioned.

"The explanation given and the verifications done allow us to rule out his participation in the facts. The investigation continues."

Mr al Hilli, an Iraqi-born engineer, his dentist wife and her mother died after their BMW was sprayed with bullets at point-blank range in a lay-by.

French cyclist Sylvain Mollier, 45, also died after being shot seven times.

Mr al Hilli's two daughters, four-year-old Zeena and seven-year-old Zainab, were in the car at the time of the shooting and survived.

The family, from Claygate in Surrey, were on a camping trip in the country.

Eric Maillaud, prosecutor in Annecy in 2012, said Zeena could not help investigators because she was hiding under her mother's legs during the attack.

Zainab was shot in the shoulder but survived and was found badly injured outside the car, where three of the bodies were found.

Some 25 cartridges were found inside the vehicle.

All of the victims had at least three bullet wounds, with each also having a single shot in the head.

Police have struggled to make progress in the case and, nine years after the attack, no charges have been filed.

In 2020, the al Hillis' daughters were set to be re-interviewed, and last year investigators returned to the murder scene, near the village of Chevaline.

Police were also investigating a possible link with a gang of contract killers living in Paris.

One theory suggested Mr al Hilli had been attacked because of his job as an engineer, while another focused on a row over a family will, but no definite motive was established.

A local dispute was considered the most likely and the family were simply and innocently caught up in it.