BOLOGNA, July 21 -- In a video that spread across Italian social media within hours of his death, Abderrahim Fakir can be heard repeating the same words: "Help, help, that's enough." Four officers hold him face-down against the pavement in Bologna's Pilastro district. He does not get up.

Fakir, a 42-year-old Moroccan-born man, died Sunday night during a police restraint that his family and their lawyers say crossed an irreversible line. By Monday evening, hundreds of people had taken to the streets of Bologna, where police deployed tear gas and water cannons to push back crowds that had gathered near police headquarters and in several neighborhoods across the city.

The Italian prosecutors' office has opened a manslaughter investigation ...