(CNN) — An airline employee stole an otherwise unoccupied passenger plane Friday from the Seattle-Tacoma International Airport and flew it for an hour with military jets chasing him before crashing in a wooded area 40 miles away.

The 29-year-old ground service agent died, the Pierce County Sheriff’s Department said, without further identifying him.

The 76-seat Horizon Air turboprop plane took off without authorization around 8 p.m. local time, with an unauthorized Horizon Air employee at the controls, airport officials tweeted.

After flying and doing air stunts for about an hour, the plane crashed at Ketron Island, the sheriff’s department said.

The man “was doing stunts in air or lack of flying skills caused crash into Island,” sheriff’s spokesman Ed Troyer tweeted. The incident was not considered terrorism, the FBI’s Seattle office said.

Authorities initially identified the man as a mechanic but later said he was a ground service agent, a job that includes directing aircraft for takeoff and gate approach, and de-icing planes.

“Our hearts are with the families of the individual aboard as well as all of our Alaska Air and Horizon Air employees,” said Constance von Muehlen, the airline’s chief operating officer.

The regional airline, based at the Seattle-Tacoma airport, is owned by the Alaska Air Group.

‘Let’s try to land that airplane safely’

In audio recordings of the incident posted on Broadcastify, air traffic controllers can be heard trying to guide the man to land the plane.

“Congratulations, you did that, now let’s try to land that airplane safely and not hurt anybody on the ground,” an air traffic controller said.

The man responded: “Awwww-right … dammit.. I don’t know man! I don’t know! I don’t want to. I was kinda hoping that was gonna be it. Ya know?”

The exchange happened during the flight, but the timing of the conversation is unclear.

The sheriff’s department described the man as suicidal. It did not elaborate.

F-15 jets chased the plane

Within minutes of the plane’s takeoff, the military scrambled two F-15 jets from Oregon to follow it, authorities said. They pursued the aircraft before it went down on Ketron Island, between Tacoma and Olympia.

F-15 “pilots kept plane out of harms way and people on ground safe,” the sheriff’s office tweeted. The jets were not involved in the crash, it said.

Washington Gov. Jay Inslee thanked the fighter pilots for keeping residents safe.

“Those pilots are trained for moments like tonight and showed they are ready and capable,” he said in a tweet.

Witness thought it was an air show

Witnesses described the surreal scene after the plane left the airport. John Waldron was walking along a trail near the bay when he noticed the two military jets following a plane that appeared to be doing acrobatics.

“I thought they were practicing for an air show,” he said.

After the plane approached Ketron Island, Waldron saw a thick column of smoke followed by a loud explosion, he said.

“Everyone was literally frozen in place, muttering about what possibly happened,” he said.

Kethleen Reichel said she watched the planes pass by for about two minutes.

“My husband and I are recently former Boeing employees, and we were wondering why a jet was near the passenger airplane,” she said. “We heard the jet because our windows were down while we were waiting in the ferry line to go to Anderson Island, which is adjacent to Ketron Island.”

Federal agencies are investigating

The plane was taken from a maintenance position and was not scheduled for a passenger flight, said Gary Beck, Horizon Air’s president and chief executive officer.

It crashed about an hour after it was stolen and did not hit any ground structures.

Several federal agencies are investigating the incident, said Brad Tilden, the chief executive officer of Alaska Air Group.

“We’re working to find out everything we possibly can about what happened, working with the Federal Aviation Administration, the Federal Bureau of Investigation, and the National Transportation Safety Board. We are giving those investigators our full support and cooperation,” Tilden said in a statement.

Normal operations at the airport were interrupted briefly, the airport said.

The plane was a Q400, a Bombardier turboprop plane, one of about 40 the airline has in its fleet.