Zimmerman verdict: Civil rights groups express dismay
Civil rights groups in the US have expressed dismay after neighbourhood watchman George Zimmerman was found not guilty of murdering black teenager Trayvon Martin in Florida last year.
The case sparked a fierce debate in the US about racial profiling.
Mr Zimmerman's family and lawyers have said they now fear he could face revenge attacks.
President Barack Obama called for calm, saying the death was a tragedy for America, but that "a jury has spoken".
"I know this case has elicited strong passions. And in the wake of the verdict, I know those passions may be running even higher," Mr Obama said in a statement.
He asked Americans to respect the Martin family's call for calm reflection and to ask "if we're doing all we can to widen the circle of compassion and understanding in our own communities".
"We should ask ourselves if we're doing all we can to stem the tide of gun violence that claims too many lives across this country on a daily basis.
"We should ask ourselves, as individuals and as a society, how we can prevent future tragedies like this. As citizens, that's a job for all of us. That's the way to honour Trayvon Martin."
Prosecutors had argued that Mr Zimmerman, 29, opened fired on 26 February 2012 because he racially profiled Trayvon Martin as he walked through his neighbourhood wearing a hooded sweatshirt in the rain, and assumed he was up to no good.
Trayvon Martin was African-American. Mr Zimmerman identifies himself as Hispanic.
But the defence said he shot Trayvon Martin in self defence after the teenager had punched their client, slammed his head into the pavement and reached for Mr Zimmerman's gun.
Mr Zimmerman was facing possible conviction for second-degree murder or manslaughter. On Saturday he was cleared of all charges by the six-woman jury at Seminole County Criminal Justice Center in Sanford, Florida.
Defence lawyer Mark O'Mara said he was "ecstatic", and that Mr Zimmerman "was never guilty of anything except protecting himself in self defence".
"I'm glad that the jury saw it that way," he said.
Another defence lawyer, Don West, said the prosecution of his client had been "disgraceful".
"As happy as I am for George Zimmerman, I'm thrilled that this jury kept this tragedy from becoming a travesty," he said.
However, following the verdict, protest marches were staged in US cities including San Francisco, Philadelphia, Chicago, Washington and Atlanta.
In Oakland, California, some protesters started small fires and smashed windows.
Civil rights leader Jesse Jackson told CNN on Sunday: "I remain stunned at the decision. The Department of Justice must intervene to take this to another level."
In a Facebook posting, he said "the American legal system has once again failed justice". But he also appealed for calm, saying anyone seeking to "compound our pain with street justice" would do "damage to the innocent blood and legacy of Trayvon Martin".
Rights activist Al Sharpton also appealed for calm, but said the verdict was "a slap in the face to the American people".
He compared the case to the beating of African-American man Rodney King by police in 1991, which sparked widespread rioting.
A petition launched by the National Association for the Advancement of Colored People (NAACP), demanding that the DoJ open a civil rights case against Mr Zimmerman, had received more than 350,000 signatures by midday on Sunday.
The petition says that "the most fundamental of civil rights - the right to life - was violated the night George Zimmerman stalked and then took the life of Trayvon Martin".
Daryl Parks, lawyer for the Martin family, told BBC News he hoped the case would be a wake-up call for the US.
"Many will realise that if there is a law that would allow you to kill an unarmed teenager, then that's a law that we probably should look at and change," he said.
Florida police had angered many by not arresting Mr Zimmerman for six weeks after the shooting, citing the state's controversial "stand your ground" law, which allows a citizen to use lethal force if he or she feels in imminent danger.
But Mr Parks said the trial had given the US "a new perspective on black life - when a young black person gets killed, the approach that it takes to investigate, to arrest the person that did it".
Meanwhile Mr Zimmerman's family and representatives have said they are afraid he could fall victim to revenge attacks.
His brother, Robert said he had received frequent threats on social media and there was "more reason now than ever to think that people are trying to kill him".
"He's going to be looking over his shoulder the rest of his life," he said.