The vigil was held at the bus depot where the 37-year-old, schizophrenic man was allegedly beaten nearly to death by six officers in early July. Thomas later died.
The names of the six officers involved in the incident were made public in a blog.
Those officers are reportedly receiving death threats. Some of them have been staying at hotel rooms.
"As far as death threats against the individual officers, they need to die as far as I'm concerned. I'm not advocating someone go out and kill them. I want it done in the court system," said Thomas' father, Ron Thomas.
With public pressure building, a second Fullerton City councilman is asking Fullerton's police chief to step down.
"Right now, I'm requesting him to resign. But at some point if he chose not to, it could turn to a termination," Councilman Bruce Whitaker said.
The chief has not responded to requests to resign.