"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, Atlanta and other cities 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. Additional demonstrations were scheduled across the country through Sunday evening.
Churches also made note of the verdict Sunday morning, with many leaders speaking about the case and urging peace in the aftermath. Some congregants wore hooded sweatshirts, as Martin had when he died, or shirts with the teen's picture.
Martin's killing in February 2012 unleashed debate across the U.S. over racial profiling, self-defense and equal justice. Protesters nationwide lashed out against police in the Orlando suburb of Sanford as it took 44 days for Zimmerman to be arrested. Many, including Martin's parents, said Zimmerman had racially profiled the unarmed black teen. Zimmerman identifies himself as Hispanic.
Six anonymous female jurors considered nearly three weeks of often wildly conflicting testimony over who was the aggressor on the rainy night the 17-year-old was shot while walking through the gated townhouse community where he was staying and where Zimmerman lived.
Jurors were sequestered during the trial, and they deliberated more than 15 hours over two days before announcing late Saturday night that they had reached a verdict. The court did not release the racial and ethnic makeup of the jury, but the panel appeared to reporters covering selection to be made up of five white women and a sixth who may be Hispanic.
In August 2012, defense attorney Mark O'Mara said Zimmerman and his wife, Shellie, had been living like hermits and weren't working because they feared for their safety.
After Saturday's verdict, police, officials and civil rights leaders urged peace and told protesters not to resort to violence. While defense attorneys said they were thrilled with the outcome, 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."
Those watching reacted strongly when the verdict was announced. Martin's mother and father were not in the courtroom when it was read; supporters of his family who had gathered outside yelled "No! No!" upon learning of the verdict.
Andrew Perkins, 55, a black resident of Sanford, angrily asked outside the courthouse: "How the hell did they find him not guilty?"
"He killed somebody and got away with murder," Perkins shouted, so angry he shook, looking toward the courthouse.
Trayvon Martin's brother, Jahvaris Fulton, said on Twitter: "Et tu America?" — a reference to the Latin phrase "Et tu, Brute?" known as an expression of betrayal.
In a Sunday afternoon statement, President Barack Obama called Martin's death a tragedy for America but asked that Americans respect calls for calm reflection.
"I know this case has elicited strong passions," he said. "And in the wake of the verdict, I know those passions may be running even higher. But we are a nation of laws, and a jury has spoken."