Smoke rises from a burned van in Villeneuve-la-Garenne, in the northern suburbs of Paris, early on April 20. (Geoffroy Van Der Hasselt/AFP/Getty Images)

PARIS — The riots began after a man on a motorcycle crashed into the open door of an unmarked police vehicle, a collision that landed him in the emergency room with a broken leg.

In the midst of a global health crisis, the April 18 incident in the Paris suburb of Villeneuve-la-Garenne might have gained little attention — even while there was some debate between witnesses and police about whether the door had been opened on purpose.