George Zimmerman has been acquitted of all charges over the death of black teenager Travyon Martin in Florida.
Mr Zimmerman was freed after the jury deliberated for more than 15 hours over two days in the second-degree murder trial.
The jurors notified the judge on Saturday night, shortly before 10pm local time, that they had reached a decision.
Minutes later the verdict was announced. Mr Zimmerman stood impassively as the verdict was read out.
The parents of the teenager were not in court for the verdict.
But outside the court supporters of Trayvon reacted with disappointment and anger.
Some chanted and held up a large banner saying “End racial oppression”, while others yelled “No” in disbelief at the acquittal.
The six-member, all-woman jury began deliberating at 2.30pm on Friday after spending part of the day listening to the defence closing arguments and a rebuttal from the prosecution.
The jurors considered nearly three weeks of often wildly conflicting testimony over who was the aggressor on the rainy night the 17-year-old was shot while walking through the gated townhouse community where he was staying.
Mr Zimmerman’s lawyers said the case was classic self-defence, claiming Trayvon knocked Mr Zimmerman down and was slamming the older man’s head against the concrete footpath when Mr Zimmerman fired his pistol.
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: “I’m glad this jury kept this tragedy from becoming a travesty.”
Prosecutors called Mr Zimmerman a liar and portrayed him was a want-to-be police officer and vigilante who had grown frustrated by break-ins in his neighbourhood committed primarily by young black men.
They said Mr Zimmerman assumed the teen was up to no good and took the law into his own hands.
The case divided public opinion in the United States, with even President Barack Obama commenting on the shooting. Congressman Bobby Rush wore a ‘hoodie’ in the House of Representatives in support of Trayvon.
Further criticism came from the 44-day delay before Mr Zimmerman was arrested.
After hearing the verdict, Judge Debra Nelson told the defendant he was free to go and the GPS tracking tag unit would be removed.
“You have no further business with this court,” judge Debra Nelson said.
Mr Zimmerman later hugged his family and his wife, Shellie, smiled and cried.
Fearing further social unrest over the controversial shooting, the police chief in Sanford, where Martin was shot and where the trial was held, urged peace.
State Attorney Angela Corey said she believed second-degree murder was the appropriate charge because Mr Zimmerman’s mindset “fit the bill of second-degree murder.”
“We charged what we believed we could prove,” Ms Corey said.
Second-degree murder is classed as a death that does not include specific intent to kill, and the trial centred on the state’s controversial self-defence rule of “Stand Your Ground”.