Alaska Airlines Bombardier Q-400 turbo-prop planes are parked at Seattle-Tacoma International Airport's C terminal on June 2, 2013, in Seattle, Washington.

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 aircraft so he could board and then take off Friday evening, authorities added.

It's unclear how he attained the skills to do loops in the aircraft before crashing about an hour after taking off into a small island in the Puget Sound, authorities said. He crashed nearly an hour after the plane was taken from a maintenance area, though officials said that it did not appear that the fighter jets were involved in the crash of the aircraft. In a news release issued Saturday, the North American Aerospace Defense Command said two F-15C alert aircraft were scrambled from Portland but did not fire upon the plane.

At a news conference in Seattle-Tacoma International Airport, officials from Alaska Airlines and Horizon Air said that they are still working closely with authorities as they investigate what happened.

"Safety is our No. 1 goal," said Brad Tilden, CEO of Alaska Airlines. "Last night's event is going to push us to learn what we can from this tragedy so that we can ensure this does not happen again at Alaska Air Group or at any other airline."

The bizarre incident involving a worker who authorities said was suicidal points to one of the biggest potential perils for commercial air travel: airline or airport employees causing mayhem.

"The greatest threat we have to aviation is the insider threat," Erroll Southers, a former FBI agent and transportation security expert, told The Associated Press. "Here we have an employee who was vetted to the level to have access to the aircraft and had a skill set proficient enough to take off with that plane."

Seattle FBI agent in charge Jay Tabb Jr. cautioned that the investigation would take a lot of time, and details, including the employee's name, would not be released right away. Dozens of personnel were out at the crash site, and co-workers and family members were being interviewed, he said.

There was no connection to terrorism, said Ed Troyer, a spokesman for the sheriff's department.

Video showed the Horizon Air Q400 doing large loops and other dangerous maneuvers as the sun set on Puget Sound. There were no passengers aboard.

Authorities initially said the man was a mechanic, but Alaska Airlines later said he was believed to be a ground service agent employed by Horizon. Those employees direct aircraft for takeoff and gate approach and de-ice planes, as well as handle baggage.

Southers, the aviation security expert, said the man could have caused mass destruction. "If he had the skill set to do loops with a plane like this, he certainly had the capacity to fly it into a building and kill people on the ground," he said.

Gary Beck, CEO of Horizon Air, said it wasn't clear how the man knew to start the engine, which requires a series of switches and levers. "We don't know how he learned to do that," he said.

The plane was pursued by military aircraft before it crashed on tiny Ketron Island, southwest of Tacoma, Washington. Video showed fiery flames amid trees on the island, which is sparsely populated and only accessible by ferry. No structures on the ground were damaged, Alaska Airlines said.

Troyer said F-15 aircraft took off out of Portland, Oregon, were in the air "within a few minutes," and the pilots kept "people on the ground safe."

Sheriff's department officials said they were working to conduct a background investigation on the Pierce County resident.

The aircraft was stolen about 8 p.m. Alaska Airlines said it was in a "maintenance position" and not scheduled for a passenger flight. Horizon Air is part of Alaska Air Group and flies shorter routes throughout the U.S. West. The Q400 is a turboprop aircraft with 76 seats.

The man could be heard on audio recordings telling air traffic controllers that he is "just a broken guy." An air traffic controller called the man "Rich," and tried to convince the man to land the airplane.

"There is a runway just off to your right side in about a mile," the controller says, referring to an airfield at Joint Base Lewis-McChord.

"Oh man. Those guys will rough me up if I try and land there," the man responded, later adding "This is probably jail time for life, huh?"

Later the man said: "I've got a lot of people that care about me. It's going to disappoint them to hear that I did this ... Just a broken guy, got a few screws loose, I guess."

Flights out of Sea-Tac, the largest commercial airport in the Pacific Northwest, were temporarily grounded during the drama.

The plane crashed in a heavily wooded area of thick underbrush on the island, said Debra Eckrote, the Western Pacific regional chief for the National Transportation Safety Board. The crash sparked a 2-acre wildfire.

"It is highly fragmented," she said of the plane. "The wings are off, the fuselage is, I think, kind of positioned upside down."

Investigators expect they will be able to recover both the cockpit voice recorder and the event data recorder from the plane.

White House Press Secretary Sarah Huckabee Sanders said Saturday morning that President Donald Trump is "monitoring the situation."

Royal King told The Seattle Times he was photographing a wedding when he saw the low-flying turboprop being chased by two F-15s. He said he didn't see the crash but saw smoke.

"It was unfathomable. It was something out of a movie," he told the newspaper.

—CNBC and Reuters contributed to this report.