By Erik Derr ( | First Posted: Jul 14, 2013 03:28 PM EDT

(Photo : Reuters)

George Zimmerman emerged from a Florida courthouse a free man yesterday, cleared of all charges in the shooting death of 17-year-old Trayvon Martin, back in February 2012.

His brother, Robert Zimmerman Jr., said the former neighborhood watch volunteer still had to get used to the idea he wouldn't be serving prison time for the killing, which Zimmerman, 29, has always maintained was in self-defense.

A jury of six women found him not guilty of second-degree murder late Saturday night and also declined to convict him on a lesser charge of manslaughter.

Many critics throughout the country have demonstrated disappointment and anger over Zimmerman's acquittal, prompting speculation from all corners that his freedom may indeed remain limited.

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

In August 2012, defense attorney Mark O'Mara said that because Zimmerman and his wife were frightened for their safety, they were living like hermits and were unable to work.

Then, despite calls by law enforcement and community leaders throughout the nation to remain calm yesterday, O'Mara repeated his concerns that his client's safety would be at ongoing risk.

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

Demonstrators displeased with the not-guilty verdict gathered for mostly peaceful demonstrations in Florida, Milwaukee, Washington, Atlanta and other cities overnight and into Sunday.

There were reports of broken windows and a vandalized police squad car in Oakland, Calif., authorities said.

More demonstrations are scheduled across the country later today.

Martin's killing in prompted often heated debate across the United States over racial profiling, self-defense and equal justice.

Protesters nationwide harshly criticized police in the Orlando suburb of Sanford, where the fatal confrontation happened, for waiting 44 days before arresting Zimmerman.

Many, including Martin's parents, asserted Zimmerman, who is identified as Latino and white, had racially profiled the unarmed black teen.

The sequestered jury considered nearly three weeks of sometimes over-the-top and deeply contradictory testimony over who was the aggressor on the rainy night Martin was shot while walking through the gated townhouse community where he was staying with his father and where Zimmerman lived.

The jury deliberated more than 15 hours over two days before they reached their decision just before 10 p.m. Eastern Daylight Time Saturday.

The court did not release the racial and ethnic makeup of the jury, but media accounts described the panel as five white women and possibly one Latina.

Martin's mother and father were not in the courtroom when the verdict was announced, but supporters of his family who had gathered outside yelled "No! No!" after the reading.

"How the hell did they find him not guilty?" asked Andrew Perkins, 55, a black resident from Sanford who stood outside the courthouse. "He killed somebody and got away with murder!"

Celebrities also reacted to the verdict, with Beyonce calling for a moment of silence in Martin's memory during a concert in Nashville.

Martin family attorney Benjamin Crump acknowledged the disappointment felt by Martin's supporters and asserted the teen should be regarded alongside civil rights heroes Medgar Evers and Emmett Till, as martyrs in the ongoing struggle for equal justice.

Yet, Crump said, "for Trayvon to rest in peace, we must all be peaceful."

Benjamin Todd Jealous, president of the National Association for the Advancement of Colored People, said his group has started a petition that calls of the U.S. Department of Justice to open a civil rights case against Zimmerman.

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