Washington - George Zimmerman, the former neighbourhood watch volunteer who fatally shot Trayvon Martin in a 2012 confrontation with the teenager, will not face federal charges, the Justice Department said on Tuesday.
The decision resolves a case that focused on self-defense gun laws and became a flashpoint in the national conversation about race two years before the Ferguson, Missouri, police shooting of a black teenager.
Zimmerman, who is white, has said he acted in self-defence when he shot the 17-year-old Martin during a confrontation inside a gated community in Sanford, Florida, just outside Orlando. Martin, who was black, was unarmed when he was killed.
Once Zimmerman was acquitted of second-degree murder by a state jury in July 2013, Martin's family turned to the federal investigation in hopes that he would be held accountable for the shooting.
That probe focused on whether the killing amounted to a federal civil rights violation, which would have required proof that it was motivated by racial animosity.
Although Martin's parents have said Zimmerman initiated the fight, the Justice Department said there was not enough evidence to establish that Zimmerman wilfully deprived Martin of his civil rights - a difficult legal standard to meet - or killed the teenager on account of his race.
"This decision is limited strictly to the department's inability to meet the high legal standard required to prosecute the case under the federal civil rights statutes; it does not reflect an assessment of any other aspect of the shooting," the Justice Department said in a news release announcing the decision on Tuesday.
Zimmerman's attorney, Don West, was on a flight and couldn't immediately comment on the decision.
Martin's parents were too distraught after their meeting in Miami with Justice Department officials to speak with reporters, their attorney Ben Crump said.
The Justice Department's decision not to file federal charges against Zimmerman was expected but still "a bitter pill to swallow," he said.
"What they told his family and I was that because Trayvon wasn't able to tell us his version of events, there was a lack of evidence to bring the charges. That's the tragedy," Crump said.
The February 2012 confrontation began after Zimmerman saw Martin while driving in his neighbourhood. Zimmerman called police and got out of his car and approached Martin, who was returning from a store while visiting his father and his father's fiancée at the same townhome complex where Zimmerman lived.
Zimmerman did not testify at his trial, but he told investigators that he feared for his life as Martin straddled him and punched him during the fight.
The decision to not prosecute Zimmerman comes even though Attorney General Eric Holder has made civil rights a cornerstone of his tenure, which is winding down.
The Justice Department is also moving to resolve a separate high-profile civil rights case - the August shooting by a Ferguson police officer of Michael Brown, an unarmed black 18-year-old. The killing sparked weeks of protests.
