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Prosecutor Eric Maillaud said in a statement that the arrest had been prompted by witness testimony after a sketch of an unknown man riding a motorcycle near the crime scene in southeastern France was made public in November.
France 3 television said the man arrested was from the region where the killings had occurred and that he had not previously been known to police. No other details were immediately available.
Saad al-Hilli, an Iraqi-born British engineer, was found shot dead in September 2012 with his wife and mother-in-law in their BMW car on a remote mountain road near the village of Chevaline in the Rhone-Alpes region. The body of a cyclist, Sylvain Mollier, was discovered nearby.
They were killed in what appeared to be execution-style murders from a semi-automatic pistol.
Al-Hilli's brother Zaid, who prosecutors said had feuded with his brother over an inheritance, was arrested last year in Britain on suspicion of conspiracy to commit murder. He was released in January by British police with no charges filed.
The witness who first discovered the family, a British cyclist, told investigators he had seen a motorcyclist not far from the scene. Two forest officials had also stopped a motorcyclist on the road before the killings were discovered and instructed him to turn around as the road was closed to traffic.
"Nothing allows us to state that the motorcyclist is the author of the crimes," Maillaud said last year, when his portrait was made public.
Hilli's two daughters survived the attack, despite the gunman trying to kill the eldest - seven-year-old Zainab - by beating her around the head after running out of bullets.
Four-year-old Zeena was found safe hiding beneath the legs and skirt of her dead mother in the backseat of the car.