CHICAGO (CBS) — Gunfire erupted in Ferguson, Missouri, late Sunday, setting off a chaotic chain of events that ended with police shooting an 18-year-old man on the anniversary of the death of Michael Brown.

The events unfolded following a day of peaceful demonstrations remembering Brown, the unarmed black teen shot and killed by white police officer Darren Wilson, sparking protests across the country, and shining a spotlight on police tactics.

Throughout the day Sunday in Ferguson, protests were organized and peaceful, but the calm came to a shocking end around 11:15 p.m., when dozens of gunshots rang out as Ferguson interim police chief Andre Anderson was talking to CBS affiliate KMOV-TV.

St. Louis County Police Chief Jon Belmar said four plainclothes officers had been tracking an 18-year-old man during a protest marking the death of Brown – believing that man was armed – when he approached the officers, who were in an unmarked SUV, and opened fire.

Belmar said the officers returned fire, and then chased the man on foot when he ran away. When the man turned and fired again at the officers, the officers shot back, and struck the gunman. He was critically wounded.

The St. Louis Post-Dispatch reported the man got out of surgery early Monday, and was very close with Brown.

The four officers have been placed on administrative leave while the shooting is investigated. They were not wearing body cameras, according to Belmar.

At the same time as that shooting, two groups of people exchanged gunfire on West Florissant Avenue, a business area that saw rioting and looting last year after Brown was killed. The gunfire sent protesters and reporters ducking for cover, as shots rang out for 40 to 50 seconds.

“It was a remarkable amount of gunfire,” Belmar said. The chief said the shooters were not part of the protests marking the anniversary of Brown’s death.
“They were criminals. They weren’t protesters,” he said.
A few hours later, two teens were shot in a drive-by near a memorial to Brown on Canfield Drive. The victims were expected to survive.

Before the spate of violence late Sunday night, the day had been peaceful in Ferguson, with hundreds of protesters gathering at the site where Brown was killed, and marching through the town.

Late last year, a Missouri grand jury declined to prosecute Wilson, who resigned from the department in November. In March, the U.S. Justice Department also declined to prosecute Wilson.