US attorney general says Trayvon Martin inquiry to continue
America's top prosecutor, Eric Holder, has said an investigation into the "tragic, unnecessary" death of 17-year-old Trayvon Martin will continue.
The justice department last year opened an inquiry into the unarmed black teenager's death, then stood aside to allow Florida's prosecution to proceed.
George Zimmerman, who said he opened fire in self-defence in February 2012, was cleared of murder on Saturday.
Civil rights groups have pledged further protests over the verdict.
Over the weekend, demonstrations across the country against the verdict have been mostly peaceful, with many demanding justice for Martin's family and questioning the fairness of the justice system.'Strong passions'
US Attorney General Holder said on Monday that he understood concerns about the case.
End Quote Robert Zimmerman Brother of George Zimmerman
He's going to be looking over his shoulder the rest of his life”
"The justice department shares your concern," he told a black women's college alumnae group in Washington DC, to applause. "I share your concern."
Mr Holder said he hoped the country would take the opportunity "to speak honestly about the complicated and emotionally charged issues that this case has raised".
On Monday evening a member of the jury said in an interview with CNN she believed Mr Zimmerman had good intentions but events "just went terribly wrong".
"I think George Zimmerman is a man whose heart was in the right place," the unnamed juror B37 said. "He went above and beyond what he really should have done."
She added that she believed Martin was the aggressor in the fight and screams heard in the background of an emergency call were the voice of Mr Zimmerman.
President Barack Obama has already acknowledged the case has elicited "strong passions", but emphasised: "We are a nation of laws, and a jury has spoken."'Having a movement'
On Monday, the White House said that Mr Obama would not involve himself in the justice department's decision on whether to pursue civil rights charges against Mr Zimmerman, a 29-year-old former neighbourhood watch volunteer.
The department has a long history of using federal civil rights law in an effort to continue legal proceedings against defendants who have already been acquitted in related state cases. But convictions are often tough to obtain in such cases, analysts say.
Demonstrations are being planned in up to 100 cities next Saturday in front of federal buildings.
Civil rights leader and broadcaster Reverend Al Sharpton is organising those events through his National Action Network.
"I don't care if it's 20 people. We want to show the nation that over 100 cities a week later is still demanding justice," he told the Tom Joyner radio programme. "We're not having a fit, we're having a movement."
Mr Zimmerman was found not guilty of second-degree murder and manslaughter late on Saturday.
After the verdict was announced, there were protests across the US - including in San Francisco, Philadelphia, Chicago, Washington, Boston, San Diego and Atlanta.
The biggest demonstration, in New York, attracted thousands of people.
Los Angeles Mayor Eric Garcetti has returned from a visit to the East Coast to deal with clashes in his city between police and protesters at a rally after the verdict was handed down.
Police used bean-bag rounds and made six arrests while breaking up demonstrations in the early hours of Monday morning. No injuries have been reported.
The National Association for the Advancement of Colored People has also called for civil rights charges to be filed against Mr Zimmerman.
His 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.