A police officer shot and killed a knife-wielding attacker who murdered four people at the Paris police headquarters Thursday, according to a French union official.

The attacker worked at the police headquarters located near Notre Dame Cathedral for more than 20 years as an administrative employee, Alliance Police Nationale union official Loïc Travers said, The New York Times reported.

“The motive is not yet known,” Travers said, according to The NYT.

A French police union official says four police officers have died in a knife attack carried out by an administrator at the Paris police headquarters. The attacker was shot to death. https://t.co/1nkPLt4VMW

— The Associated Press (@AP) October 3, 2019

Travers said he cannot remember an attack on police officers of this magnitude, The Associated Press reported. Paris prosecutor Remy Heitz said three officers and one administrator died.

French President Emmanuel Macron visited the headquarters Thursday to show solidarity and support for the officers, AP reported.

The attack came one day after tens of thousands of police took to the streets in protest of poor working conditions, lack of public respect and several police suicides that happened this year, The NYT reported.

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Image: Reuters.