Retaliation Possible Motive in Killing of Oklahoma Airport Worker, Police Say

— -- The man suspected of fatally shooting a Southwest Airlines employee Tuesday at Will Rogers World Airport in Oklahoma City was a former employee of the U.S. airline who may have "acted in retaliation," police said today.

Police say the suspected shooter, who was later found dead of an apparent, self-inflicted gunshot wound, had waited to ambush Michael Winchester. Investigators believe the victim was shot as he was leaving work and walking to his car Tuesday afternoon.

Winchester, 52, was transported to a hospital, where he was pronounced dead. Police said they did not know his job title. Southwest Airlines said Winchester had been with the company for 29 years.

Police said the suspected shooter, identified as Lloyd Dean Buie, was a former employee of Southwest Airlines who resigned from his post in April 2015. Police said Winchester was not his immediate supervisor.

Police said the suspect went to Will Rogers World Airport intending to harm someone and that he may have been reacting to his resignation last year.

"It is believed this crime was premeditated and that the suspect armed himself and went to the airport with the intention of shooting someone," Oklahoma City Police Department spokesman Capt. Paco Balderrama said at a news conference this morning. "We do not know if Mr. Winchester was the intended victim, but it is possible the suspect acted in retaliation against circumstances leading up to his resignation."

Southwest Airlines confirmed that Buie was a former ramp agent hired in Kansas City in November 1999 who later worked in Oklahoma City. The company said Buie had exhibited "symptoms of being under the influence of alcohol while at work" one day in April 2015. Southwest Airlines immediately request he be tested, but Buie declined and resigned.

"Our Southwest Family is grieving, as we are deeply saddened by the loss of our Family Member," the airline said in a statement today. "Our focus remains on offering support to the Winchester family and Southwest Employees during this difficult time."

Balderrama said police have not yet checked the suspect's record for any previous criminal convictions.

The airline confirmed that one of its employees had died in a statement Tuesday, saying, "It is with great sorrow that Southwest Airlines confirms that a Southwest Employee who was injured during a shooting incident today at Will Rogers World Airport in Oklahoma City has died from injuries. We continue to work with the local authorities investigating this incident."

The suspect's body was found inside a red pickup truck in a five-story parking garage at the airport with an apparent, self-inflicted gunshot wound to the head. Investigators have served a search warrant to Buie's residence in south Oklahoma City, police said.

Will Rogers World Airport has reopened since the shooting.

ABC News' Erin Dooley contributed to this report.