PARIS (AP) — Four family members of a man killed after ramming his car into a police convoy on Paris' Champs-Elysees are in custody.

The Paris prosecutor's office said Tuesday that the four were detained overnight in the anti-terrorism investigation into Monday's attack.

Police officials said the man was on police radar for ties to radicalism, and the prime minister confirmed that the man had a gun permit. Prime Minister Edouard Philippe said on BFM television Monday that the permit was initially issued before the attacker was flagged to authorities.

The man set off a fiery blast when he drove his car packed with arms and explosives into police. No one else was hurt in the incident on one of Paris' busiest shopping districts. The Champs-Elysees reopened overnight.