Stephon Clark's fiancee and his young children were among those at Saturday's rally in Sacramento, following outrage over autopsy results which showed he was shot in the back.
Reinhardt made headlines last year after he took a swipe at President Trump's immigration policies, writing in an opinion that an administration order to deport a man was "inhumane."
More protests are expected Thursday in a city that has experienced nearly two weeks of continuous unrest after the shooting of a 22-year-old unarmed black man by two police officers.
The attorney general announced a separate inquiry to review of policies, procedures and practices at the Sacramento Police Department to identify ways to achieve safer outcomes.
