George Zimmerman emerged from a Florida courthouse a free man after a jury cleared the former neighborhood watch volunteer of all charges in the fatal shooting of an unarmed black teenager in a verdict that sparked largely peaceful protests across the country.

Zimmerman’s brother said the former neighborhood watch volunteer was still processing the reality that he would not serve prison time for the killing of 17-year-old Trayvon Martin, which Zimmerman, 29, has maintained was an act of self-defense. A jury found him not guilty of second-degree murder late Saturday night and declined to convict him on a lesser charge of manslaughter.

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.

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 broke windows and vandalized a police squad car in Oakland during protests in four California cities, authorities said.

Also Sunday, the Justice Department said it was looking into the case to determine whether federal prosecutors will file criminal civil rights charges now that Zimmerman has been acquitted in the state case.

The department opened an investigation into Martin’s death last year but stepped aside to allow the state prosecution to proceed.

In a statement, the Justice Department said the criminal section of its civil rights division, the FBI and the U.S. Attorney’s office for the Middle District of Florida were continuing to evaluate the evidence generated during the federal probe, in addition to the evidence and testimony from the state trial.

“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,” the statement said. Justice added that it will determine “whether federal prosecution is appropriate in accordance with the department’s policy governing successive federal prosecution following a state trial.”

The Justice Department has a long history of using federal civil rights law in an effort to convict defendants who have previously been acquitted in related state cases.

On Sunday, NAACP President Benjamin Todd Jealous started a petition calling for the department to open a civil rights case against Zimmerman. But experience has shown it is almost never easy getting convictions in such high-profile prosecutions.

“The Justice Department would face significant challenges in bringing a federal civil rights case against Mr. Zimmerman,” said Alan Vinegrad, the former U.S. Attorney in the Eastern District of New York. “There are several factual and legal hurdles that federal prosecutors would have to overcome: They’d have to show not only that the attack was unjustified, but that Mr. Zimmerman attacked Mr. Martin because of his race and because he was using a public facility, the street.”

As to the last element, the confrontation between Zimmerman and the shooting victim occurred in a gated community, which may not fit the legal definition of a public facility.

Lauren Resnick, a former federal prosecutor in New York who successfully tried a man in the killing of an Orthodox Jew during the 1991 Crown Heights riots in Brooklyn, said the Justice Department could conceivably proceed under a theory that Zimmerman interfered with Martin’s right to walk down a public street based on his race or religion. But that would be challenging, she said, because it would require prosecutors to prove, among other things, that trailing Martin on the street constituted interference.

“One could argue it did, if it freaked him out and he couldn’t comfortably walk down the street — there’s an argument here,” said Resnick, who is now in private practice.

But she said federal prosecutors were likely to encounter the same hurdles as state prosecutors in establishing that Zimmerman was driven by racial animus and was the initial aggressor, as opposed to someone who acted in self-defense.

“When you have a fact pattern where one person’s alive, and one person’s not, and the person alive is the defendant, it’s hard to prove things beyond a reasonable doubt,” said Resnick.

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Whether or not the Justice Department steps in, it is unlikely Zimmeran’s life will return to normal soon.

Zimmerman’s defense attorneys, led by Mark O’Mara, said they were thrilled with the outcome, but O’Mara suggested Zimmerman’s safety would be an ongoing concern.

“There still is a fringe element that wants revenge,” O’Mara said. “They won’t listen to a verdict of not guilty.”