Walnut Creek, California (CNN) -- Dueling rallies took place Monday involving a former Bay Area Rapid Transit police officer who was found guilty of involuntary manslaughter in the shooting death of an unarmed passenger. Several hundred people gathered in this suburban community, some 25 miles northeast of San Francisco, with supporters of former officer Johannes Mehserle joined by critics, who said they were calling for justice for his victim, Oscar Grant. The Walnut Creek branch of the Contra Costa County Superior Court closed early Monday because of the rallies, and all cases that were scheduled to be heard Monday afternoon were postponed. Some gas stations and a restaurant in the area also opted to close down for the day.
@highlight
NEW: Police Lt. says crowds were vocal but orderly
@highlight
No arrests as opposing groups demonstrate over transit killing
@highlight
Groups demonstrate about a transit officer who shot and killed an unarmed black man
@highlight
Officer was found guilty of involuntary manslaughter in the shooting of Oscar Grant
"I work across the street from the @placeholder, and I'm not concerned at all."