OLYMPIA, Wash. (AP) — Investigators are piecing together how an airline ground agent working his regular shift stole an empty Horizon Air turboprop plane, took off from Sea-Tac International Airport and fatally crashed into a small island in the Puget Sound after being chased by military jets that were quickly scrambled to intercept the aircraft.

Officials said Saturday that the man was a 3.5-year Horizon employee and had clearance to be among aircraft, but that to their knowledge, he wasn't a licensed pilot. The 29-year-old man used a machine called a pushback tractor to first maneuver the ai...