He is a former small-town cop with a bad temper, a big gun collection and a resemblance to a person seen near a mass homicide scene in the French Alps.
Now working as a security guard, the 48-year-old former French gendarme was taken into custody on Tuesday and is now being questioned in connection with the sensational 2012 killings of three members of a British family who were on a camping trip as well as a passing cyclist.
However, French prosecutor Eric Maillaud, speaking to reporters on Wednesday, warned that the homicides had not been solved.
Mr. Maillaud confirmed that investigators were tipped about the man because he looked like the composite sketch of a helmeted biker seen near the scene of the killings.
He said police have since established that the man's cellphone pinged a transmission tower in a location that would have made it possible for him to be at the crime scene.
The man collected vintage Second World War weapons, among them a German-made Luger P08 pistol that used 9mm bullets.
The murder weapon was, however, a Swiss-made Luger P06 that fired 7.65mm Parabellum bullets.
About 40 firearms, a grenade and an artillery shell were found when the police searched the man's properties. "He's likely involved in arms trafficking. Whether that was for collection or for criminal aims, we do not know yet," Mr. Maillaud said.
A close friend of the man was also arrested as he tried to flee the police, who found weapons, ammunition, explosives and a detonator at his house, the prosecutor added.
The arrest is the newest twist in the highly publicized killings in the Haute-Savoie region, an hour's drive from Geneva.
Saad al-Hilli, 50, his 47-year-old wife, Iqbal, and her mother, Suhaila al-Allaf, 74, were each shot twice in the head while they were in the family BMW at the end of a winding road near the village of Chevaline.
A passing cyclist, Frenchman Sylvain Mollier, who might have arrived in mid-shooting, was also killed.
Mr. al-Hilli was found slumped over the steering wheel of his car, the engine still running. The woman were shot dead in the back seat.
The eldest daughter, seven-year-old Zainab, was seriously wounded and collapsed in front of the vehicle when a passerby saw the crime scene and called police.
Rescuers who opened the car's door then found the youngest child, four-year-old Zeena, who was alive and had been hiding for hours under her mother's body.
For months, as investigators looked at links in France, Britain and the Middle East, various theories floated about what could have happened.
Could Mr. al-Hilli been targeted because was of Iraqi ancestry or because of his work as an aerospace engineer?
What if, instead of being a collateral victim, the French cyclist, Mr. Mollier, was actually the real target of the killer? The father of three worked for a company that manufactured metal alloys for nuclear reactors.
Or was it Mr. al-Hilli's brother, Zaid? The two men had been feuding over an inheritance. Zaid al-Hilli was questioned and released last summer.
On Wednesday, Mr. Maillaud said Zaid al-Hilli remained a suspect.
"There are still investigations into other aspects, the family angle, the Iraqi angle, we are not closing doors," the prosecutor said.
The latest turn in the case started in November with the release of a composite sketch of a goateed, helmeted motorcyclist who had been seen by witnesses near the shooting.
It was quickly noted that the helmet in the portrait was a GPA brand model that was manufactured in small numbers because it was used only by French law-enforcement officers.
The arrested man was a former municipal police officer in the small town of Menthon-Saint-Bernard. Mr. Maillaud was not sure if the man had resigned or been fired a year ago.
The prosecutor also acknowledged that the man was known for his bellicose attitude and that there had been allegations that he made threatening remarks to tourists. "He could have had a peculiar personality, that doesn't make him a killer," he cautioned.
Under French law, the man can be held for questioning for up to four days.