OKLAHOMA CITY (AP) — Oklahoma City police investigators are trying to figure out why a man waited to gun down an airline employee outside Will Rogers World Airport in an ambush that prompted authorities to shut down the state's busiest airport for hours.

Police Capt. Paco Balderrama says the suspected shooter was found dead inside a pickup truck on Tuesday from an apparently self-inflicted gunshot wound. They believe he watched airport employees come and go before shooting and killing 52-year-old Michael Winchester, a Southwest Airlines employee.

Balderrama said late Tuesday that investigators hadn't positively identified the shooter, but that the man apparently knew Winchester's schedule and routine and that the two men likely knew one another.

The 1 p.m. shooting set off a scramble at the airport, with police immediately closing the sprawling complex.