MONTREAL—Anti-police demonstrators solemnly marched past the site of a tragic shooting where two people — including an innocent bystander — were killed by officers’ bullets.

Then they began smashing windows Wednesday night.

Members of the crowd picked up materials from a construction site and hurled them as projectiles. They pelted bricks and chunks of concrete at about a dozen commercial store windows, attacking businesses like restaurants and coffee shops. Several of the windows shattered.

An outdoor portable toilet was overturned and tossed into the street.

Many of the 200 protestors were dressed head to toe in black or wore black bandanas to conceal their faces, garb commonly worn at rowdy protests. Some later shed their dark clothing to blend back in with the peaceful protestors.

They chanted slogans and held signs denouncing police violence. One giant banner said, “Never again.”

Dozens of police officers on motorcycles kept an eye on the crowd. The city has a history of violence at anti-police protests.

This march was prompted by tragic events Tuesday: police shot and killed two people — a homeless man allegedly wielding a knife, and an innocent bystander who was on his way to work at a hospital.

Just before it turned unruly, the crowd paused solemnly at the site of the shootings just outside the Universite du Quebec a Montreal. One man speaking into a megaphone reminded fellow protestors that the blood of the victims was still visible on the rain-soaked sidewalk.

“I’m here to demonstrate against police impunity,” said another protester who would only call himself George.

“Cops investigating cops over these shootings — it just doesn’t work, man.”

Numerous critics are calling for a change in the way Quebec investigates police-related shootings. Presently in the province, any shooting involving an officer’s gun is investigated by an outside police force. Tuesday’s shootings by Montreal police are being investigated by the provincial force.

Critics say the system lacks transparency.

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In a bizarre twist, reports emerged just as the protest began that Quebec provincial police officers were involved in another shooting in the town of Rawdon, Que.

Two policewomen intervened to help a man who, police say, had been attacked. After an altercation, provincial police say one of their officers fired at the lower body of a man causing the disturbance. The man was brought to hospital; his injuries were not considered life-threatening.