Protesters shout slogans during a demonstration in Ferguson, Missouri, the United States, on Aug 15, 2014. [Photo/Xinhua]

Brown's death had already ignited several days of clashes with furious protesters. Tensions eased Thursday after Nixon turned oversight of the protests over to the Missouri Highway Patrol. Gone were the police in riot gear and armored vehicles, replaced by the new patrol commander who personally walked through the streets with demonstrators. But Friday night marked a resurgence of unrest.

Local officers faced strong criticism earlier in the week for their use of tear gas and rubber bullets against protesters. Johnson said one tear gas canister was deployed Friday night after the group of rioters became unruly.

The officer who killed Brown was identified as 28-year-old Darren Wilson, a six-year police veteran who had no previous complaints filed against him.

The Ferguson Police Department has refused to say anything about Wilson's whereabouts, and Associated Press reporters were unable to contact him at any addresses or phone numbers listed under that name in the St. Louis area.

Wilson has been on paid administrative leave since the shooting. St. Louis County prosecutor Bob McCulloch said it could be weeks before the investigation wraps up.

St. Louis County Executive Charlie Dooley asked Missouri Attorney General Chris Koster on Friday to take over the case, saying he did not believe McCulloch could be objective. Koster said Missouri law does not allow it unless McCulloch opts out, and McCulloch spokesman Ed Magee said the prosecutor has no plans to surrender the case.