The acquittal of a white former police officer sparked protests in St. Louis on Sept. 16. (Monica Akhtar/The Washington Post)

After a third night of violence and unrest in St. Louis, about 100 protesters  marched in silence along downtown streets Monday during the morning rush hour. Once they reached City Hall, the silence gave way to chants for justice.

The city has been marked by protests since Friday, when former police officer Jason Stockley was acquitted on charges of murdering a black motorist after a police chase in 2011. Stockley is white.

Overnight Sunday, police arrested more than 80 people after a peaceful protest turned violent as night fell. In a concentrated area downtown, some protesters smashed windows and overturned trash cans, while others threw chemicals and rocks at police, authorities said.

“After the demonstration, organizers announced that the daytime protest was over,” Mayor Lyda Krewson said in news conference at about 1 a.m. Monday. “But a group of agitators stayed behind, apparently intent on breaking windows and destroying property.”

She declined to take reporters’ questions.

Some protesters complained that police were unnecessarily aggressive. Further inflaming tensions, a St. Louis photographer reported he and others heard police chant “whose streets, our streets” after making some arrests.

The photojournalist, David Carson, later tweeted that he’d spoken to the commander at the scene, who said that he did not hear the chant but that it was unacceptable and he would “deal with it.”

The Associated Press also independently reported on the police chanting. The phrase used is commonly chanted by demonstrators, particularly Black Lives Matters protesters.

At around 11:20 p.m. Sunday, the St. Louis Metropolitan Police Department’s Twitter feed said “multiple warnings to disperse” had been given near the intersection of Washington Avenue and North Tucker Boulevard. They soon started arresting those that hadn’t left.

But several protesters said police had encircled them and there was no way out. Caught in the melee was St. Louis Post-Dispatch reporter Mike Faulk, who tweeted, “Less than 100 of us including media blocked in at wa and Tucker on all four sides.”

Shortly afterward, Faulk was among those arrested. In a photo, he appeared to be wearing a media badge around his neck at the time of his arrest.

Interim Police Chief Lawrence O’Toole repeatedly referred to those arrested as “criminals” during a news conference overnight Sunday.

“These criminals that we’ve arrested should be held accountable and prosecuted to the fullest extent of the law,” he said. “We’re in control. This is our city and we’re going to protect it.”

O’Toole said some officers incurred “moderate or minor” injuries, but didn’t say how many were hurt.

“I’m proud to tell you the city of St. Louis is safe and the police owned tonight,” he said. “Once again, a group of criminals set out to break windows and destroy property. Tonight, those criminals are in jail.”

According to local media, about 1,000 people had gathered outside a downtown police station before sunset and marched peacefully before nightfall. The violence appeared to erupt about 8 p.m. as a small group broke away and began smashing windows at several businesses.

Those protesters were eventually greeted by police officers dressed in riot gear. Police said they gave demonstrators an hour’s notice before making the mass arrests just before midnight.

A man throws a rock into the window as during protests in St. Louis on Sept. 17. (AP)

Earlier Sunday, news outlets reported that the Department of Justice had opted not to pursue a federal civil rights prosecution of former officer Stockley. The decision was made a year ago, but the department waited to announce it until after Friday’s verdict in the criminal case.

Stockley, 36, was charged in May 2016 with first degree murder in the fatal shooting of 24-year-old Anthony Lamar Smith after a police chase. Stockley and his partner had pursued Smith by vehicle after failing in an attempt to arrest him for a suspected drug deal at a Church’s Chicken.

Prosecutors said in a videotape during the chase, Stockley was heard saying “Going to kill this motherf—er don’t you know it” before telling his partner to drive into Smith’s slowing car. Prosecutors also suggested Stockley had planted a gun in the vehicle since the weapon contained the officer’s DNA, but not Smith’s.

In a 30-page ruling issued Friday, St. Louis Circuit Judge Timothy Wilson said he had agonized over his decision. “This Court, as the trier of fact, is simply not firmly convinced of the defendant’s guilt,” he said.

Protests erupted almost immediately on the streets of St. Louis.

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