Lyon - French police on Tuesday arrested a 48-year-old man as part of their investigation into the 2012 murders of a British-Iraqi family and a cyclist in the Alps, the local prosecutor said.
Annecy prosecutor Eric Maillaud said the man, from the Haute-Savoie region, was placed in formal custody and was detained following the release in November of an identikit image of a mysterious motorcyclist seen near where the quadruple murder took place.
"This arrest, which may not be the only one, was the result of witness statements" that came in after the image was released, Maillaud said.
He said there was no apparent "direct link" between the man and the victims.
A source close to the investigation said police were carrying out a search of the man's home near the scene of the crime, in the presence of his girlfriend.
The source described him as "taciturn mountain man" and a gun enthusiast who lives on the fringes of society.
Maillaud said the man bore a "strong resemblance" to the man in the identikit image.
It is the first time anyone has been arrested in France in connection with the case, which has stumped investigators despite major efforts on both sides of the English Channel.
Saad al-Hilli, a 50-year-old Iraqi-born British tourist, was gunned down in September 2012 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 multiple 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 gruesome attack, but the older girl was shot and badly beaten.
The younger girl survived unscathed after hiding under her mother's skirts for hours after the killings, initially escaping the notice of police.
A 45-year-old French cyclist, Sylvain Mollier, was also killed after apparently stumbling on the scene.
Saad al-Hilli's brother Zaid was arrested in Britain in June last year on suspicion of conspiracy to commit murder but police said last month there was insufficient evidence to press charges.
Investigators had been looking at an inheritance dispute between the two brothers but Tuesday's arrest focused attention on the possibility of a local killer.
The source close to the case said the arrest was "an important step forward in the investigation" but added that "other arrests should follow."
French police can hold suspects in criminal cases for up to 48 hours without charge.
The source was cautious about the arrest, noting the lack of any links to the victims.
"This is someone who lives around Chevaline and who has no known employment," the source said. "He was someone that investigators were looking at as part of their local leads."
The identikit image released in November featured a man sporting a goatee and wearing a rare type of motorcycle helmet.