FERGUSON, Missouri (AFP) - Fury mounted in the US town of Ferguson on Tuesday as the family of a slain black teenager denounced the "broken" justice system that failed to indict the white policeman who shot him.
Lawyers for the family of Michael Brown, backed by civil rights leaders, denounced the prosecutor whose grand jury hearing found that the officer had killed the 18-year-old in self-defense.
Rioting, looting and arson attacks erupted in Ferguson overnight after the decision, despite a huge deployment of police and state troopers, and the St Louis suburb was braced for more to come.
"This process is broken. This process should be indicted," lawyer Benjamin Crump declared at an impassioned news conference called after the night of chaos fed America's racial tensions.
Crump criticised the way Officer Darren Wilson had not been cross-examined when he appeared before the grand jury which decided not to indict him over the August shooting.
"When was his credibility ever challenged?" he asked.
Crump also denounced what he called the "symbiotic relationship" between St Louis County prosecutor Robert McCulloch, who is the son of a slain police officer, and local law enforcement.
Civil rights firebrand Reverend Al Sharpton said the Brown case renewed a nationwide fight for greater police accountability.
"This is not a Ferguson problem ... This is a problem all over the country," he said. "We may have lost one round but the fight is not over. They have broken our hearts, but not our backs." And, as protest marches continued to spread in other US cities, Sharpton warned that on Saturday there would be nationwide protests by the black community and civil rights supporters.
Brown's family had appealed for calm, but Monday night's eruption of fury in Ferguson rapidly degenerated into looting, arson and running street battles between police and stone-throwers.
Protesters shot at police, robbed locally-owned stores and set cars and buildings ablaze in what police said was the worst violence since Wilson shot Brown on August 9.
The August shooting sparked weeks of protest and a nationwide debate about military-style police tactics and race relations.
On Tuesday morning, the streets of Ferguson were all but deserted, with very few people in the streets and a police helicopter buzzing overhead. Police tried to stop reporters entering the riot-hit area Missouri officials said they were increasing police presence and vowed to respond swiftly to any further violence.
"You will see a large police presence and when crime starts you'll see... an intervention much more quickly than we did last night," police chief Sam Dotson told reporters Tuesday morning.
Dozens of people were arrested and at least 12 buildings and two police cars were set ablaze Monday as groups of youths roamed the streets looting stores and spreading mayhem.
But no one was killed or seriously hurt and police did not open fire at any point, St Louis County police chief Jon Belmar said.
The Ferguson grand jury concluded Wilson had acted lawfully in firing 12 shots at Brown after he first reached into the officer's car to grapple with him then turned on him as he gave chase.
Ferguson is a mainly black suburb with a mainly white police force and Brown's death, and the aggressive police response to initial protests and now the result of the grand jury hearing have stirred tensions.
The town's African American community of 21,000 has been on edge since the shooting, and residents complain of years of racial prejudice and heavy handed police tactics.
As riot officers responded to protesters with tear gas, batons and flash grenades, Pat Bailey, a retiree from St Louis in her 60s, said she had expected the decision.
"I've lived long enough to know that African Americans are not considered human beings," Bailey said.
In Washington, President Barack Obama made a rapidly-organised televised appearance to appeal for calm, echoing the sentiments of the dead teenager's family.
"Michael Brown's parents have lost more than anyone. We should be honoring their wishes," Obama said.
Some witnesses had said in August that Brown had his hands up and was surrendering when he was killed. But McCulloch said the physical evidence and other witnesses contradicted this account.