US President Barack Obama appealed for calm after an acquittal in the killing of black teenager Trayvon Martin, saying: "We are a nation of laws, and a jury has spoken.''
What began as a confrontation on a rainy February night between a neighbourhood watch volunteer and a teenage boy walking home from a grocery store rapidly turned into a heated and polarising national debate about race, profiling, guns and self-defence.
George Zimmerman, the Florida neighbourhood watch captain who shot and killed 17-year African American high school student Trayvon Martin in a killing that raised major questions about race and gun control in America, was yesterday found not guilty of his murder.
It prompted an outpouring of outrage on twitter and protests around the US including in Washington DC, Chicago, San Francisco and Los Angeles.
Obama: 'Respect call for calm'
Obama, who had spoken emotively on the case before, noting that if he had a son he would have "looked like Trayvon Martin,'' reiterated that the impact of the death went much wider than the Florida town of Sanford.
"The death of Trayvon Martin was a tragedy. Not just for his family, or for any one community, but for America. I know this case has elicited strong passions. And in the wake of the verdict, I know those passions may be running even higher.''
"I now ask every American to respect the call for calm reflection from two parents who lost their young son,'' he said.
He tied the killing of the teenager to the problems surrounding gun use in the United States, an issue on which the president tried but failed to push through new control measures earlier this year.
"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,'' Obama said.
"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 honor Trayvon Martin.''
Dramatic trial, 16 hours deliberation and not guilty verdict
After a dramatic three-week trial and more than 16 hours of deliberation, the all-woman jury in Sanford, Florida, reached a not guilty verdict after deciding that the 29-year-old had acted in self-defence when he shot and killed Martin.
Zimmerman remained expressionless as the verdict was read out with his family members smiling broadly. The Martin family, who had pushed so publicly for an investigation into their son's death, were not in the court as the verdict was read out.
The judge told Zimmerman he was free to go, telling him that the GPS beacon that had been tracking him while on bail would be switched off as he left the court.
"We're ecstatic with the results," defence lawyer Mark O'Mara said after the verdict. "George Zimmerman was never guilty of anything except protecting himself in self-defence."
Another member of his defence team, Don West, said he was pleased the jury "kept this tragedy from becoming a travesty".
How it unfolded
The shooting in a gated community in a town of 50,000 people 50km north of Orlando, caused a national public outcry last year after the Martin family and civil rights leaders alleged police had failed to properly investigate Zimmerman, who was not arrested until 44 days after the shooting.
The black teenager had been walking to his father's house after buying some sweets at the local shop when he was seen by Zimmerman, who called the police but ignored the orders of police dispatchers not to confront the boy. A fight then ensured during which Zimmerman shot Martin dead.
News of the shooting caused a furore which led to the sacking of Sanford's white police chief, even drawing in President Barack Obama who said that if he had a son "he'd look like Trayvon", sparking a national debate over race relations in America more than 20 years after the infamous beating of Rodney King.
However, as time passed and more details emerged about Zimmerman, whose mother is Hispanic, the racial tensions surrounding the case eased.
The family's demands for a full investigation and trial were met and a new, black police chief, Cecil Smith, was installed in Sanford with a mission to promote even-handed policing.
Martin supporters express anger
Yesterday, supporters of Trayvon Martin's family gathered outside the court to await the verdict expressed anger and disappointment at the outcome.
Bernie de la Rionda, the assistant state attorney who was the chief prosecutor in the case against Zimmerman, said he and his two fellow prosecutors were unhappy about the outcome of the trial.
"I am disappointed, as we are, with the verdict. But we accept it," he said.
"We live in a great country that has a great criminal justice system. It's not perfect, but it is the best in the world Call for calm after not-guilty verdict and we respect the jury's verdict," he said.
Before the verdict both families, civil rights leaders including Jesse Jackson, and local police had all called for a calm response to a case that has riveted America over the last three weeks.
The trial turned on several key defence witnesses who appeared to support Zimmerman's claims that he had acted in self-defence and shot Martin as an act of last resort after the teenager banged his head repeatedly into the concrete pavement, a claim consistent with his head injuries.
In one of the most telling testimonies, forensic pathologist Vincent DiMaio said that examination of the bullet wound had supported Zimmerman's contention that Martin was on top, straddling him during the fight.
Also central to the trial was the question of whether it was Zimmerman or Martin that was heard screaming for help on an emergency call moments before the fatal shot was fired.
Experts from the FBI ruled that with Martin dead, it was impossible to prove scientifically who was screaming.
Among some black residents of Sandford, there was anger and sadness at the verdict.
Community leaders have added their calls for calm.