A jury's decision to clear George Zimmerman in the death of Trayvon Martin has been greeted with outrage and a barrage of questions.
As President Barack Obama and civil rights leaders urged calm, thousands of demonstrators across the United States protested the not-guilty verdict, decrying it as a miscarriage of justice.
"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 Sunday. "But we are a nation of laws, and a jury has spoken."
Here's more on the Florida case that has become a national emotional flashpoint:
What was the essence of the case?
There was never any doubt that Mr. Zimmerman, now 29, fatally shot Mr. Martin, 17. But the case hinged on whether the neighbourhood watch volunteer had acted in self-defence when he met the teenager inside a gated community in the central Florida town of Sanford on the night of Feb. 26, 2012.
Mr. Zimmerman, who identifies as Hispanic, called police after spotting Mr. Martin from his car, believing the black teenager in a hoodie to be suspicious. Mr. Martin, who was staying at the home of his father's fiancée, was walking back from a convenience store where he had bought Skittles and a can of iced tea.
Minutes later, after Mr. Zimmerman got out of his car, the two engaged in a fight that left Mr. Zimmerman with a bloody nose and cuts and scrapes on the back of his head. The encounter ended when Mr. Zimmerman shot Mr. Martin once through the heart with a 9mm pistol.
Why did the jury acquit Zimmerman?
The jury of six women considered nearly three weeks of often wildly conflicting testimony over who was the aggressor. They deliberated for more than 15 hours over two days before finding Mr. Zimmerman not guilty of second-degree murder and manslaughter late Saturday night.
The jurors had to sort out clashing testimony from 56 witnesses in all, including police, neighbours, friends and family members. None had a clear view of the encounter. For example, witnesses who got fleeting glimpses of the fight in the darkness gave differing accounts of who was on top. And both Mr. Martin's parents and Mr. Zimmerman's parents claimed that the person heard screaming for help in the background of a neighbour's 911 call was their son.
Prosecutors had to prove that Mr. Zimmerman committed a crime in pursuing and killing Martin and that he did not act in self-defence, a bar they failed to clear with jurors. They portrayed Mr. Zimmerman as a "wannabe cop" vigilante who had grown frustrated by break-ins in his neighbourhood committed primarily by young black men. Mr. Zimmerman assumed Mr. Martin was up to no good and took the law into his own hands, they said, ignoring a dispatcher's instruction not to follow the teen.
To secure a second-degree murder conviction, prosecutors had to convince the jury that Mr. Zimmerman acted with a "depraved" state of mind — that is, with ill will, hatred or spite. Prosecutors said he demonstrated that when he muttered, "F------ punks. These a-------. They always get away" during a call to police as he watched Mr. Martin walk through his neighbourhood.
To win a manslaughter conviction, prosecutors had to convince the jury only that Zimmerman killed without lawful justification.
Defence attorneys said the case was classic self-defence, claiming Mr. Martin knocked Mr. Zimmerman down and was slamming the older man's head against the concrete sidewalk when Mr. Zimmerman fired his gun.
"We're ecstatic with the results," defence attorney Mark O'Mara said after the verdict. "George Zimmerman was never guilty of anything except protecting himself in self-defence."
What role did race play in the trial?
One of the few mentions of race came from witness Rachel Jeantel, the Miami teen who was talking to Mr. Martin by phone moments before he was shot. She testified that he described being followed by a "creepy-ass cracker" as he walked through the neighbourhood.
Ms. Jeantel gave some of the trial's most riveting testimony. She said she overheard Mr. Martin demand, "What are you following me for?" and then yell, "Get off! Get off!" before his cellphone went dead.
What was the role of Florida's self-defence law?
Mr. Zimmerman wasn't arrested for 44 days after the shooting as Sanford police insisted that Florida's Stand Your Ground law on self-defence prohibited them from bringing charges. Florida gives people wide latitude to use deadly force if they fear death or bodily harm.
Mr. Martin's parents, along with civil rights leaders, argued that Mr. Zimmerman had racially profiled their son. And they accused investigators of dragging their feet because Mr. Martin was a black teenager.
Before a special prosecutor assigned to the case ordered Mr. Zimmerman's arrest, thousands of people staged protests, with many demonstrators wearing hoodies and carrying Skittles. Mr. Obama also weighed in, saying: "If I had a son, he'd look like Trayvon."
Could Zimmerman face other charges?
The Justice Department is looking into the case to determine whether federal prosecutors should file criminal civil rights charges now that Mr. Zimmerman has been acquitted in the state case. The department opened an investigation into Mr. Martin's death last year but stepped aside to allow the state prosecution to proceed.
The evidence generated during the federal probe is still being evaluated by the criminal section of the Justice Department's civil rights division, the FBI and the U.S. Attorney's office for the Middle District of Florida, along with evidence and testimony from the state trial, the Justice Department said in a statement.
The National Association for the Advancement of Colored People is collecting signatures on an online petition calling for federal civil rights charges.
"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. We ask that the Department of Justice file civil rights charges against Mr. Zimmerman for this egregious violation," the petition says.
As well, NAACP president Benjamin Jealous said Mr. Martin's family may bring a civil suit against Mr. Zimmerman.
With reports from The Associated Press and Reuters