6.50pm BST

Veteran civil rights leader, the reverend Al Sharpton, began his address at the foot of police headquarters in New York City with a chant; "I am Trayvon Martin", Ryan Devereaux writes.

The crowd before him, numbering well into the hundreds, immediately repeated his words.

"We're standing up today for justice for Trayvon Martin," Sharpton said. He said he would join a march to Washington DC next month in support of a wide range of racial justice issues, saying demonstrators would number "tens of thousands".

Sharpton recalled the moment he first heard of the shooting that left an unarmed, 17 year-old Trayvon Martin dead.

"I'd never heard of Sanford," he said, referring to the town where Martin died. "But I heard too many times of stories where people are killed and treated like they are worthless, and it was a sense of justice that we said that this man should not be let go."

Sharpton introduced Sybrina Fulton, Trayvon Martin's mother, who took the microphone with her remaining son, Jaharvis, standing nearby.

"I am honored that you all decided to take part in this occasion," she began. She paused as she continued to thank the crowd, appearing to struggle for words.

"We love you," a woman yelled. Others cheered and applauded.

Fulton went on to describe how she felt her son was portrayed in the trial that acquitted his killer, George Zimmerman.

"Trayvon was a child," Fulton said. "I think sometimes it gets lost in the shuffle because as I sat in the courtroom, it made me think they were talking about another man. And it wasn't. It was a child."

"He was always a child. He acted as a child. He behaved as a child," she said. "And don't take my word for it, he had a drink and candy."

"Not only do I vow to you to do what I can for Trayvon Martin," she told the crowd. "I promise you I'm going to work hard for your children as well."

In closing, Fulton encouraged supporters to express their voices "in a peaceful manner ... so we can change some of these laws."