(Bloomberg) -- Alaska Air Group Inc. said an employee stole an empty passenger plane from its main hub in Seattle, and some witnesses said they saw it making unusual maneuvers over Puget Sound, tailed by fighter jets, before crashing.

The 76-seat turboprop, a Horizon Airlines Q400, had no passengers or crew aboard, other than the person who made the unauthorized takeoff Friday night, Alaska said. A spokesman for the Pierce County Sheriff’s Department, which includes Tacoma and the crash site near Ketron Island, said on Twitter that preliminary information indicates the thief was a “suicidal” mechanic.

The incident temporarily halted flights at Sea-Tac International Airport, which is among the busiest in the U.S. by passenger traffic. Alaska Air is based in Seattle, and owns the Horizon Air regional operation. Delta Air Lines Inc. also has been expanding its presence at the airport.

A widely circulated eye-witness video uploaded to Twitter on Friday evening shows a turboprop flying low as the sun sets over Puget Sound. A voice can be heard exclaiming, “That is not a drone. That is a real plane. It just did a loop-de-loop.” At least one fighter jet then enters the picture.

Ed Troyer, a spokesman for the Pierce County Sheriff’s Department, said the plane appeared to be doing stunts or may have gone down due to a “lack of flying skills.” F-15s were scrambled out of Portland, Oregon, and a loud noise heard over Puget Sound was the military’s sonic boom, not an explosion, he wrote on Twitter. Investigators are looking into the 29-year-old suspect’s background, Troyer said, without identifying the man.

“We believe it was taken by a single Horizon Air employee,” Horizon Air Chief Operating Officer Constance von Muehlen said in a video statement. “Our hearts are with the family of the individual aboard, as well as all our Alaska Air and Horizon Air employees.”

A message from Horizon Air Chief Operating Officer Constance von Muehlen: https://t.co/BDhk9pf1Yt

— Alaska Airlines (@AlaskaAir) August 11, 2018

The plane was on the ground for maintenance before the incident and wasn’t scheduled for a passenger flight, the airline later said in an additional statement. No buildings were involved in the crash.

The Federal Bureau of Investigation said it didn’t appear to be an act of terrorism, though its investigation would continue.

The man was heard telling air-traffic controllers that he is “just a broken guy,” the Associated Press reported. “I got a lot of people that care about me and it’s gonna disappoint them to hear that I did this.”

The U.S. Coast Guard sent a vessel to the crash scene where a large plume of smoke was visible, the AP said.

By 9:30 p.m., Sea-Tac Airport said normal operations had resumed.

To contact the reporters on this story: Noah Buhayar in Seattle at nbuhayar@bloomberg.net;Sarah Jacob in Bangalore at sjacob19@bloomberg.net

To contact the editors responsible for this story: Michael J. Moore at mmoore55@bloomberg.net, David Scheer, John McCluskey

©2018 Bloomberg L.P.