Deputies said Anthony Craig Chambers boarded the bus on Santa Monica Boulevard in West Hollywood Sunday, drew a shotgun from a suitcase and shot 51-year-old Alan Thomas twice. Thomas worked for the MTA for five years.
Chambers was arrested minutes later. The exact motive behind the shooting remains unclear. If convicted, Chambers could face the death penalty. He is currently being held on $1 million bail.
He is scheduled to be arraigned June 12 in Beverly Hills.
A candlelight vigil was held Monday night for Thomas, who leaves behind a wife, mother and an adult son.