The sheriff's office in Broward County, in the Miami area, said it had made a contingency plan to respond to incidents tied to a verdict, as it used a public service announcement to urge people to refrain from violence or destruction.
"Freedom of expression is a constitutional right," the sheriff's office said. "While raising your voice is encouraged, using your hands is not."
The Rev. Jesse Jackson Jr., a prominent civil rights leader, was among those who urged people not to react with violence.
"If Zimmerman is convicted there should not be inappropriate celebrations, because a young man lost his life, and if he is not convicted we should avoid violence because it will only lead to more tragedies," Jackson said.
But O'Mara, for one, said that whatever the outcome, his client will not feel safe.
"There are a percentage of the population who are angry, they're upset, and they may well take it out on him," he said.