The grand jury found there was no probable cause to charge Ferguson, Missouri, police officer Darren Wilson, who is white, with any crime for the shooting of 18-year-old Michael Brown, an incident that highlighted longstanding racial tensions in the predominantly black city, which has a white-dominated power structure.
"They determined that no probable cause exists to file any charge against officer Wilson," St. Louis County Prosecutor Bob McCulloch told reporters in Clayton, Missouri, a suburb of St. Louis where the grand jury met.
Brown's family said they were "profoundly disappointed" by the grand jury's finding.
"While we understand that many others share our pain, we ask that you channel your frustration in ways that will make a positive change," the family said in a statement released by its attorneys.
A crowd of several hundred people gathered outside the Ferguson Police Department ahead of the news, and many began to scream angrily as the news of the grand jury's decision was read.
Authorities had stepped up security in and around Ferguson ahead of the decision, and Missouri Governor Jay Nixon called up the National Guard to guard against the kind of rioting that flared in the weeks after the Aug. 9 shooting.
Ahead of the decision, officials called on area residents to remain calm following the grand jury's decision.
"This is not the time to turn on each other," St. Louis County Executive Charlie Dooley told a news conference.
Dooley said he did not want residents to feel they need to barricade themselves in their homes. "I do not want people to accidentally shoot or harm someone out of fear," Dooley said.
The grand jury, with nine white and three black members, began meeting in late August and heard evidence that included witnesses called by the prosecution as well as a private pathologist hired by the Brown family to review the shooting. Nine jurors needed to agree to bring charges.
Lawyers for Brown's family say the teen was trying to surrender when he was shot, while Wilson's supporters say he feared for his life and opened fire in self-defense. Brown was shot at least six times.
Brown is suspected of having stolen cigars from a nearby convenience store shortly before the incident. Brown and a friend had been walking down the middle of the street when Wilson approached them, though police said in August that Wilson was not aware of the robbery at the time.