Leonel Gutierrez is free on bond and will be sentenced on Nov. 1. Victim-impact statements will be read at that time.
The 18-year-old faces up to nearly five years in prison.
Wactor was shot and killed in May.
He was ending his bartending shift in downtown Los Angeles when he saw thieves trying to steal his car's catalytic converter.
Three other people have been charged in connection to Wactor's death. Two of them are charged with murder and one with being an accessory after the fact, in addition to robbery and gun charges.
They've pleaded not guilty and are due in court next month.