For safety reasons, BART trains are bypassing the Fruitvale station while the protest continues. Organizers say the rally will last until 8 p.m.
Rally organizer Evan Shamar said Grant "was executed right here while he was hogtied" and vowed "we will not be silent."
Shamar said BART police officer Johannes Mehserle, who shot Grant after he and other officers responded to a report that two groups of men were fighting on a train, "should be prosecuted for second-degree murder."
There was a loud cheer when Shamar announced to the crowd, "We just got word that the officer (Mehserle) has resigned."
But Shamar said there's still unfinished business, saying, "We want him charged in an American courtroom."
The crowd then chanted, "No justice, no peace!"
Protesters booed when Leslie Littleton, Oakland Mayor Ron Dellums' deputy chief of staff, read a statement from Dellums in which the mayor said, "Our entire community grieves at the loss of Oscar Grant III" and "I am profoundly saddened by the turn of events that resulted in the loss of a young man's life which has left a family and a community."
The protesters said they think that Dellums should have been at the rally to speak for himself.
Littleton told the crowd that Dellums couldn't attend the rally because he was holding a news conference at City Hall to talk about Grant's shooting death.
Rally organizers said they will have another protest at BART headquarters at 9 a.m. Thursday when the transit agency's board of directors has a meeting.
