A man killed four people in a knife attack on Paris police headquarters on Thursday before being shot dead at the building.
Paris prosecutor Remy Heitz said three men and a woman were killed. A fifth person was critically injured and has had emergency surgery in hospital.
Mr Heitz said three of the dead were police officers and the fourth was an administrative assistant.
He said the attacker's home was being searched and that authorities were for now ruling out a terrorism inquiry.
The attack came a day after police across the country went on strike complaining about work conditions and high levels of violence against officers.
The incident took place about midday in central Paris close to the city's famous cathedral, Notre-Dame.
The attacker, 45, was an employee at the police station in the IT department. The motive for his attack was not immediately clear.
French Interior Minister Christophe Castaner said the attacker was known to colleagues and worked with the police since 2003.
"He never presented any behavioural issues," Mr Castaner said outside the police station. "He never presented the slightest cause for alarm before going on his deadly rampage today."
He said that police were "particularly stricken by this exceptionally grave incident".
The man ha problems with his supervisor, a police official told Franceinfo radio.
"Did he snap, or was there some other reason? It's still too early to say," Loic Travers, head of the Alliance Police union for the Paris region, told BFM television.
French President Emmanuel Macron went to the scene alongside Prime Minister Edouard Philippe and Mr Castaner.
Mr Macron’s office said the president was there to show solidarity and support towards all police officers and employees.
Police union leader Jean-Marc Bailleul described the incident as criminal rather than an act of terrorism.
"It was a moment of madness," Mr Bailleul said.
Paris Mayor Anne Hidalgo tweeted that her thoughts went out to the family and relatives of the victims.
On Wednesday, thousands of police officers took part in the "march of anger" in Paris to protest against working conditions, which they said led to dozens of suicides in the force.
Officials claimed that more than 50 officers had killed themselves since the start of the year.
It was the first mass police strike in France since 2001.
