Miami was one of 100 cities that hosted a rally for "National Justice for Trayvon Day" on Saturday.
The rally was held on the plaza of the Wilkie D. Ferguson, Jr. United States Courthouse.
The Rev. Al Sharpton's National Action Network said the goal of the "100 City Campaign" is to urge the Justice Department to consider a federal civil rights prosecution in the death of Trayvon Martin.
George Zimmerman, a Hispanic man, shot the African-American teenager on February 26, 2012. He claimed self-defense, and a Florida jury acquitted him July 13.
Zimmerman had a confrontation with Martin after calling police to report a suspicious person. The case became a flashpoint in debates over racial profiling.
Saturday's rallies were headlined by Martin's mother, Sybrina Fulton, her surviving son, Jahvaris Fulton, and Sharpton in New York.
Many wore T-shirts bearing the slain 17-year-old's image and waved signs at the Miami gathering. Some brought their children.
Martin's father, Tracy, spoke at the rally outside a downtown federal courthouse.
"This could be any one of our children," he said. "Our mission now is to make sure that this doesn't happen to your child."
He recalled how he vowed to Martin as he lay in his casket that he would seek justice.
"I will continue to fight for Trayvon until the day I die," Martin said. "Not only will I be fighting for Trayvon, I will be fighting for your child as well."
Rallygoer Shantescia Hill carried a sign that read: "Everyone deserves a safe walk home."
The 31-year-old mother, who is black, said she wants to see Florida's "stand your ground" law repealed. "I'm here because our children can't even walk on the streets without fearing for their lives," she said.
As Hill spoke, an organizer shouted through a loudspeaker and the crowd repeated her words.
"I am Trayvon's mama!" the leader shouted.
"I am Trayvon's mama!" the crowd responded.
Karline Raphael, 40, a teacher from Miami, came with her 17-year-old daughter and 16-year-old niece.
"We wanted to show our support to the parents," Raphael said. "We're still living in a racial society. ... We see every day that we're still living in racially segregated areas."
Her daughter, Lee-Ana, agreed.
"When I found out about the verdict, I really felt something," she said. "People do look at you and judge you based on your skin color."
Speaking about the case Friday, President Barack Obama said it is a reality for black men in American to "be followed in a department store" while shopping or to walk down the street and "hear the car doors lock." The nation's first black president said he had both experiences before he rose to social and political prominence.
Attorney General Eric Holder announced this week that his department would investigate whether Zimmerman could be charged under federal civil rights laws. Zimmerman's lawyers have said their client wasn't driven by race, but by a desire to protect his neighborhood.
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