A California immigration official opened fire on his supervisor in a Long Beach federal building, and was shot dead in turn by a fellow agent, sources have told the Los Angeles Times. The supervisor was seriously injured but was in stable condition last night, according to officials. The cause of the confrontation wasn't immediately revealed. The shootings at the offices of the Immigration and Customs Enforcement agency—the main enforcement arm of the Department of Homeland Security—triggered a massive response from local cops and the FBI. (More Immigration and Customs Enforcement stories.)