ERGUSON, Mo. (AP)-- A white police officer will not face charges for fatally shooting an unarmed black teenager in a case that set off violent protests and racial unrest throughout the nation, an attorney close to the case said Monday night.

A St. Louis County grand jury declined to indict officer Darren Wilson, 28, for firing six shots in an August confrontation that killed 18-year-old Michael Brown, said Benjamin Crump, an attorney for the family. The decision had been long awaited and followed rioting that resembled war-zone news footage in this predominantly black suburb of St. Louis.

"The jury was not inclined to indict on any charges,'' Crump said after being informed of the decision by authorities. Prosecutors scheduled an news conference to announce the decision.

Missouri Gov. Jay Nixon, a Democrat, called for calm after calling up National Guard troops to stand by in case of unrest. Speaking before the decision was announced, he urged that "regardless of the decision, people on all sides show tolerance, mutual respect and restraint.''

Crowds gathered around the Ferguson police headquarters in anticipation of the announcement at the courthouse in Clayton, Mo., another St. Louis suburb.

The 12-person grand jury had been considering whether probable cause existed to bring charges against Wilson, 28, the white officer who fatally shot Brown, an 18-year-old black man, after their Aug. 9 confrontation. The shooting inflamed tensions in a largely minority community that is patrolled by an overwhelmingly white police force.

Brown's lifeless and bleeding body lay for more than four hours in a Ferguson residential street after the shooting, prompting dismay and anger as a crowd gathered. Protests turned into rioting and looting the following night, and police responded with armored vehicles and tear gas, triggering a nationwide debate over police tactics.

The 12-person grand jury, including nine whites and three African Americans, had been meeting in secret for months, hearing evidence and weighing whether Wilson's should face charges that could have ranged from involuntary manslaughter to murder.

Brown's family joined thousands of protesters to demand Wilson's arrest. As anger at official inaction grew following Brown's death, protesters clashed with police, who began patrolling the streets with military-grade weapons and armored vehicles.

Wilson has been on paid leave and largely invisible since the shooting.

While the grand jury met in secret to hear evidence in the case, two starkly different versions of the events leading to the shooting emerged in media accounts.

Police have said a scuffle broke out after Wilson asked Brown and a friend to move out of the street. Wilson told investigators he shot Brown only after the teenager reached for the officer's gun. Some witnesses

said Brown had run away from Wilson, then turned and raised his hands in the air in a gesture of surrender before he was shot in the head and chest.

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