The U.S. Department of Justice said Sunday it would review the Travyon Martin-George Zimmerman case to determine if it should consider prosecuting Zimmerman, who was acquitted in a Florida court in the shooting death of the unarmed black teenager.

"Experienced federal prosecutors will determine whether the evidence reveals a prosecutable violation of any of the limited federal criminal civil rights statutes within our jurisdiction, and whether federal prosecution is appropriate in accordance with the Department's policy governing successive federal prosecution following a state trial," said a statement released by the department.

The announcement came just barely an hour after U.S. President Barack Obama urged for "calm reflection."

In a statement released on Sunday afternoon, Obama called the case a "tragedy" for America and asked the public to remain calm, urging respect for the Martin family.

'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.'—U.S. President Barack Obama

"I know this case has elicited strong passions. And in the wake of the verdict, I know those passions may be running even higher," he said. "But we are a nation of laws, and a jury has spoken. I now ask every American to respect the call for calm reflection from two parents who lost their young son." 

"We should ask ourselves if we’re doing all we can to widen the circle of compassion and understanding in our own communities. 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. We should ask ourselves, as individuals and as a society, how we can prevent future tragedies like this."

The six women jurors who deliberated for 16 hours over two days found Zimmerman not guilty of second-degree murder and manslaughter Saturday night in a case that has polarized the U.S. public.

Zimmerman's brother said the former neighborhood watch volunteer was still processing the reality that he wouldn't serve prison time for the killing of Martin, which Zimmerman, 29, has maintained was an act of self-defense.

However, with many critics angry over his acquittal, his freedom may be limited.

"He's going to be looking over his shoulder the rest of his life," Robert Zimmerman Jr. said during an interview on CNN.

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Darrsie Jackson reacts after hearing the verdict of not guilty in the trial of George Zimmerman with her children at the Seminole County Courthouse. (John Raoux/Associated Press)

Demonstrators upset with the verdict protested mostly peacefully in Florida, Milwaukee, Washington, D.C.,  Atlanta and elsewhere overnight and into the early morning Sunday, but some protesters broke windows and vandalized a police squad car in Oakland during protests in four California cities, authorities said. Additional demonstrations were scheduled across the country through Sunday evening.

Thousands of protesters chanting "No justice, no peace" gathered in New York City on Sunday to protest the acquittal.

"I feel if we don't step it up, we're in trouble," said Prince Akeem, 20, of the Bronx. "It's young blacks being targeted and we have to stand up, stand up to the cops."

In Manhattan, congregants at Middle Collegiate Church were encouraged to wear hooded sweatshirts in the memory of Trayvon Martin, the unarmed black teenager who was wearing a hoodie the night he was shot to death in February 2012.   The Rev. Jacqueline Lewis, wearing a pink hoodie, urged peace and told her congregation: "We're going to raise our voices against the root causes of this kind of tragedy."

At a youth service in Sanford, Fla., where the trial was held, teens wearing shirts displaying Martin's picture wiped away tears during a sermon at the St. Paul Missionary Baptist Church.

In Florida, about 200 demonstrators marched through downtown Tallahassee carrying signs that said "Racism is Not Dead" and "Who's Next?"

'There is reason to be concerned that race was a factor in why he targeted young Trayvon.'—Benjamin Jealous, NAACP

Debates about racial profiling, guns, self-defense laws and the equality of justice that arose from the 2012 shooting continued the morning after the verdict.

Civil rights activist Jesse Jackson had earlier called for the Department of Justice to intervene.

"I remain stunned at the decision," civil rights leader Jesse Jackson said on CNN earlier Sunday. "The [U.S.] Department of Justice must intervene to take this to another level."

'Race was a factor'

Benjamin Jealous, president of the National Association for the Advancement of Colored People, said Sunday he had spoken to senior Justice officials about pursuing federal civil rights charges against Zimmerman.

"When you look at comments made by young black men who lived in that neighbourhood about how they felt especially targeted by [Zimmerman], there is reason to be concerned that race was a factor in why he targeted young Trayvon," Jealous told CNN.

The jurors were sequestered during the three weeks of testimony and remained anonymous by court order. They declined to speak to reporters after the verdict.

Defense lawyers had argued that Martin, 17, attacked Zimmerman on the night of Feb. 26, 2012, in a gated community in Sanford, Florida. Prosecutors had to prove that Zimmerman committed a crime in pursuing Martin and that he did not act in self-defense.

The court unshackled Zimmerman from an electronic monitoring device that he had been wearing while on bail. Zimmerman, who had received death threats, now faces a possible civil wrongful death lawsuit from Martin's family.

The tense drama that had been building for 16 months climaxed with the late-night reading of the verdict when a court clerk said "not guilty." Zimmerman, 29, showed no emotion at first, but later broke into a smile after sitting down.

No arrest sparked outrage

Outrage over the case was triggered by the refusal of the police department in the central Florida town to arrest Zimmerman after the shooting, believing his story that he acted in self-defense when he shot Martin.

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Hanna Brianna, 5, holds a sign in front of her home in Sanford, Fla. (Mike Brown/Associated Press)

Protests began in Sanford and soon spread around the country, creating pressure that forced the Sanford police chief to step down and led Florida's governor to appoint a special prosecutor, who brought a second-degree murder charge 45 days after the shooting.

Zimmerman, who is white and Hispanic, spotted Martin from his car inside the gated community where he was a neighborhood watch coordinator and called police, believing Martin to be suspicious. The teenager was staying in the neighborhood, the house guest of his father's fiancee.

Minutes later, after Zimmerman got out of his car, the two engaged in a fight that left Zimmerman with a bloody nose and head injuries. The encounter ended when Zimmerman shot Martin once through the heart with a 9mm pistol.

Some critics said special prosecutor Angela Corey overcharged the case by alleging second-degree murder, saying the lesser charge of manslaughter was more appropriate.

The acquittal will weaken any wrongful death civil lawsuit that Martin's family might bring. Such a case would have a lower burden of proof and Zimmerman, who opted against taking the witness stand in his criminal trial, might be forced to testify.

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Patrick Woodburn, left, and William Memola hold signs supporting George Zimmerman in front of the Seminole County Courthouse. (Phelan M. Ebenhack/Associated Press)

"We will seek and get immunity in a civil hearing," said Zimmerman's lead defense lawyer, Mark O'Mara.

Civil rights leader Al Sharpton called the verdict "a slap in the face to the American people" and urged federal action.

He cited the example of Rodney King, the man whose videotaped beating by Los Angeles police triggered rioting two decades ago after a state criminal trial found the police officers not guilty. Later, the Justice Department prosecuted some of the officers in a federal civil case.

Demonstrators outside the Seminole County Courthouse where the trial was held chanted "No justice, no peace" before and after the verdict, and the activist group Act Now to Stop War and End Racism called demonstrations on Sunday in New York, Boston, San Francisco and other cities.

Celebrities pay tribute

The trial's outcome was noted in the world of music.

Beyonce called in a concert for a moment of silence for Trayvon Martin, rapper Young Jeezy released a song in Martin's memory and Russell Simmons called for peace.

'Put that energy into challenging these horrible laws that allow overly-anxious neighbourhood watchmen to carry guns and shoot innocent people.'—Russell Simmons on Twitter

Beyonce took a moment to honour Martin during her Mrs. Carter Show World Tour concert at Bridgestone Arena in Nashville, Tenn. Her concert started about 30 minutes after the Zimmerman verdict began to circulate.

"I'd like to have a moment of silence for Trayvon," the pop star said as the stage grew dark with just a few key lights shining.

It Young Jeezy posted a new song, It's a Cold World (A Tribute to Trayvon Martin,to his Facebook page with a comment: "I am in no way shape, form, or fashion ... trying to capitalize off of the latest series of events. These are my true feelings and my form of expression about it."

Simmons, a producer and entrepreneur, posted a blog entry that said he'd be supporting the Trayvon Martin Foundation in helping to repeal laws like Florida's Stand Your Ground law. He signed off, "God bless you little brother. Rest in peace."

"If u have any anger this evening," Simmons wrote on Twitter, "put that energy into challenging these horrible laws that allow overly-anxious neighbourhood watchmen to carry guns and shoot innocent people. "