The protesters rallied in support of a schizophrenic homeless man who was severely beaten by six Fullerton officers during an arrest in July.
Kelly Thomas, 37, was taken off life support days after the beating.
"We think the protest movement is the only thing that has pushed the city to take measures such as having the chief go on medical leave, bringing in an independent investigator, but we don't want it to stop here," said Ian Thompson, an organizer with the ANSWER Coalition. "There has to be full justice."
The six officers involved in the arrest have been placed on paid leave.
There have also been calls for several public officials to step down, including the city mayor.
An outside independent investigator has been brought in to assess the department's policies and procedures. The FBI and the Orange County District Attorney's Office are also investigating Thomas's death.