On 3 October 2019, a police employee at the Paris police headquarters stabbed four of his colleagues to death and injured two others. He was shot dead by police at the scene.

During the early afternoon of 3 October 2019, a police agent stabbed six colleagues at the Prefecture of Police on the Île de la Cité in central Paris, killing three police officers and one member of the support staff as well as injuring two others.

Police opened fire, killing the attacker in the building's main courtyard.

 The attack came a day after police went on strike across France over increasing violence towards officers.

The attacker was reported as being 45-year-old Mickaël Harpon, an IT specialist who worked in the intelligence unit of the police headquarters for the last 16 years and held a military secrecy security clearance, giving him access to restricted information like the watchlist of terror suspects, addresses of police officers and data on French citizens and their families who had returned after they fought in the Syrian Civil War.

 He was born in Fort-de-France in the Caribbean overseas department of Martinique in 1974, and had been deaf since childhood.

 The murder weapon was a ceramic knife of a type undetectable by metal scanners.

Initial reports suggested a workplace dispute was the motive. The day after the attack, a counter-terrorism investigation was opened, looking into whether the attacker was a radicalised Islamist and the possibility of having been in contact with or received support from any terrorist groups. The perpetrator had converted to Islam; according to Paris prosecutor Jean-François Ricard his conversion to Islam took place a decade prior.

 He attended mosque rituals twice a day.

 Colleagues had reported Harpon in 2015 for voicing support for the attack on Charlie Hebdo; nothing was done.

The counter-terrorism head said that the attacker had radical and extremist religious views, that started when he justified some violent acts with an Islamist background, stopped wearing Western clothes and to not talking to other women excluding those of his family. Ties between Harpon and Salafist men were also confirmed.

 Before starting the attack, Harpon talked with his wife, and they exchanged a total of 33 messages. Among those, Harpon wrote "Allah Akbar" and "Follow our much-loved Prophet Muhammad, and meditate on the Quran".

A USB flash drive was found at Harpon's office: propaganda material from the Islamic State of Iraq and the Levant, including beheading videos, and details of police officers who worked with him were found inside it. Officers are now investigating possible links with the 2016 Magnanville stabbing, in which two police officers were killed at their home by Larossi Abballa, an Islamist who pledged allegiance to the Islamic State.