"The detention ended today at 1730 (1630 GMT)," prosecutors in southeastern town Annecy said in a statement, adding that "the explanations offered and checks carried out allowed his possible involvement in the events to be ruled out".

The detention of the unnamed man had raised hopes of a breakthrough in one of the country's most notorious murder cases that saw three members of a British family gunned down in front of their two young daughters.

A French cyclist was also killed nearby on a remote mountain road near Lake Annecy.

Prosecutors had earlier Thursday said that the suspect had participated in a reconstruction of the crime scene three months ago as a witness.

Meanwhile local newspaper Le Dauphine Libere identified the arrested man as a mystery motorcyclist seen near the scene of the crime who was cleared in 2015 after a more than two-year hunt by police to find him -- although prosecutors declined to confirm whether it was the same man.

French investigators have continued to work on the more than nine-year-old cold case, but have always struggled to identify a motive for the killings of the Al-Hilli family.

"Investigations are continuing to find the perpetrator or perpetrators of the crime," prosecutors said on Thursday afternoon, adding that three people were working on the case full time.

Saad al-Hilli, a 50-year-old Iraqi-born British tourist, was gunned down along with his 47-year-old wife Iqbal and her 74-year-old mother in a woodland car park close to the village of Chevaline in the hills above Lake Annecy.

Each was shot several times in their British-registered BMW estate car and more than two dozen spent bullet casings were found near the vehicle.

The couple's two daughters, aged seven and four at the time, survived the attack, but the older girl was shot and badly beaten.

A 45-year-old French cyclist, Sylvain Mollier, was also killed after apparently stumbling upon the scene.

- 'Cleared in 2015' -

A lawyer for the arrested man said on Wednesday evening that the detention was unjustified as his client had already been "cleared in 2015" after being spoken to as a "mere witness".

Lawyer Jean-Christophe Basson-Larbi told reporters that his client's position remained he was in the area at the time and never crossed paths with the Al-Hilli family.

After being questioned in 2015, the motorcyclist was said by the local prosecutor to be "the head of a business in the Rhone-Alps region, with a good reputation and above any suspicion, who had gone to do some paragliding and was on his way home."

Police eventually tracked him down after releasing an image showing him with a goatee and wearing an unusual type of helmet.

He told police that he had not come forward as a possible witness because he had not been paying attention to the media.

He was tracked down after police gathered all 4,000 mobile phone numbers logged in the area on the day of the murders and began ringing each one.

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