Kentucky ? A 25-year-old press operator shot and killed five co-workers and himself at a plastics plant in rural western Kentucky just hours after arguing with his supervisor about not wearing safety goggles and using his cell phone while on the assembly line, police said Wednesday.

Authorities said Wesley N. Higdon of Henderson was so riled by the argument with his supervisor that he called his girlfriend and told her that he wanted to kill his boss. The girlfriend didn’t warn anyone, police said, and just two hours later he argued with another co-worker at a gas station near the plant, then returned and shot and killed his supervisor as they walked outside. He went back inside and shot at co-workers in a break room and on the plant floor before turning the gun on himself.