ER Season 6 Episode 22 May Day ( Air Date 2000-05-18 ) Genre Drama category. Overview "As the result of a school shooting, Kovac and Benton care for the gunman and his victims. Abby discovers that Carter has been illegally injecting pain relievers. Greene and Weaver confront Carter about his problem, and Weaver orders him to enter a drug rehabilitation center or leave the hospital permanently.".