A 31-year-old French police officer shot three people dead before turning the gun on himself, in a killing spree sparked by a row with his girlfriend, authorities said Sunday.
The news comes with France already grappling with a surge in police suicides this year.
The Paris officer, Arnaud Martin, finished his shift on Saturday evening and went to meet his girlfriend in Sarcelles, a suburb north of the capital city, to discuss ending their relationship.
But after an argument broke out, Martin shot the young woman in the face and killed two men, aged 30 and 44 who attempted to intervene, said Eric Corbaux, prosecutor for the Pontoise department.
He then went to his girlfriend's home just a few yards away, where he killed the girl's father and seriously injured her mother in the throat.
He also shot the woman's sister in the leg and killed the family dog.
The attacker was later found "dead from a gunshot wound to the head, his gun in his hand, in the back of the garden," Corbaux said.
His former girlfriend was in a stable condition in hospital on Sunday, while her mother was described as "critical", he added.
"According to his superiors, he was a good civil servant, a very serious former gendarme," Corbaux said.
A source close to the investigation told AFP that investigators will need to focus on whether the attack was premeditated, but said there was "no element" to suggest that at this stage.
Saturday's tragedy comes as French officials confront a sharp increase in police suicides, with more than 45 officers and 16 gendarmes killing themselves so far this year.
Interior Minister Gerard Collomb told France Inter radio that the attacker was "someone who, at one point, totally derailed. He was armed, he could fire."
But Collomb said he would not backtrack on allowing officers carry their weapons when off-duty, a practice France introduced after the November 2015 terror attacks in Paris.
"It's something that requires a lot of attention by police supervisors," Collomb said, though he acknowledged that most police suicides are prompted by events in their private lives.