Hundreds of police officers in riot gear mobilized in downtown St. Louis after another day of peaceful protests over an ex-police officer's acquittal in the death of a black man, a scene that grew ugly after nightfall amid dozens of arrests and reports of property damage and vandalism in the streets.

Authorities made the arrests shortly before midnight, saying people had ignored orders to disperse after the peaceful protests.

A judge ruled Friday that Jason Stockley, a 36-year-old who left the department and moved to Houston three years ago, was not guilty in the 2011 death of Anthony Lamar Smith. The ruling set off raucous protests throughout the weekend.

On Sunday, hundreds of people marched through downtown streets, the posh Central West End, and the trendy Delmar Loop area of nearby University City. Protesters also marched through two shopping malls in a wealthy area of St. Louis County. The protest began at the police headquarters downtown.

Following the same pattern of the previous days, well over 1,000 people marched peacefully for several hours. By nightfall, most had gone home. The 100 or so demonstrators who remained grew increasingly agitated as they marched toward the core of downtown. Along the way, they knocked over planters, broke windows at a few shops and hotels, and scattered plastic chairs at an outdoor venue.

According to police, the demonstrators then sprayed bottles with an unknown substance on officers. One officer suffered a leg injury and was taken to a hospital. His condition wasn't known.

The recent St. Louis protests have followed a pattern borne of months of angry and sometimes violent protests after the 2014 killing of Michael Brown in nearby Ferguson: The majority of demonstrators, though angry, are law-abiding. But as the night wears on, a subsection emerges, a different crowd more willing to confront police, sometimes to the point of clashes.

More than 50 people were arrested over the weekend, all late at night. It was after nightfall that people shattered a window at the home of Mayor Lynda Krewson on Friday, smashed about two dozen windows and threw trash cans and rocks at police in University City on Saturday, and knocked out windows downtown on Sunday.

Many protesters believe police provoked demonstrators by showing up in riot gear and armored vehicles; police said they had no choice but to protect themselves once protesters started throwing things at them.