The families of Michael Brown and Eric Garner were among the demonstrators yesterday in the heart of the US capital Washington for the "Justice For All March," part of a growing protest movement sparked by the fatal August shooting of the unarmed Brown, 18.
A grand jury decision last month not to indict police officer Darren Wilson over the killing in Ferguson, Missouri, was followed by another that also declined to charge another white policeman in the Staten Island "chokehold" death of father-of-six Garner.
Rice's family and relatives of Trayvon Martin -- shot and killed in Florida by a neighborhood watchman in 2012 -- were also at the Washington march, which was mirrored by crowds that flooded downtown New York in protest.
Thousands more gathered in chilly Manhattan, shutting down major roads, with protesters shouting "We will shut New York City down" and "Black lives matter."
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Bartender Cole Fox, 24, marched with his mother and held a banner reading, "Grand Jury Reform Now."
"Fundamental changes need to be made. It's just a matter of days before the next person, black or white, is killed," he said.
Student Rosalind Watson, 21, decried "institutional racism."
"If one person sees this march and feels more supported and safe, it'll be a success," she said at the spirited protest.
Demonstrators also turned out in Berkeley, California, where an effigy of a black man was hung by a noose at the entrance of a university with the words "I can't breathe" scrawled on its chest.