Alaska Air's website says its Q400 propjets - flown by its subsidiary, Horizon Air - hold 76 passengers and are used for short-haul flights.
PCSO confirmed in a tweet that the person is a "suicidal male" and is a 19-year-old Pierce County resident.
In a video posted to Alaska Airlines' verified YouTube page late Friday night, Horizon Air's Chief Operating Officer, Constance von Muehlen, said the plane was taken by a Horizon Air employee, and no other passenger or crew were onboard.
An aircraft that took off without authorization and without passengers has crashed, officials at Seattle-Tacoma International Airport said Friday night.
Flights from Sea-Tac were temporarily grounded but normal operations resumed around 9:30 p.m. The mechanic was either "doing stunts in air" or "his lack of flying skills caused crash into [Ketron] Island".
Officials said the plane later crashed into the sea.
Evacuations still in place as fire grows overnight
Sherwood said no witnesses have come forward saying they saw Clark start the fire, but the area of origin is around his residence. According to reports from the scene, the first firefighter fell and fractured his knee, and the other twisted his ankle.
The plane was chased by military aircraft, witnesses said.
Two F-15s fighter jets pursued the plane but were not involved in the crash, local TV station KIRO7 reported. It crashed on the south of Ketron Island, near a military facility. I don't know man!
"Congratulations, you did it", the control tower tells the pilot, according to audio that aired on CNN.
"I felt like we were on the ground and we were safe, we weren't in the sky while something was going on", he said after getting off the plane.
"We saw the jets circle back after and she texted that there was no plane", she added. The sheriff said he was probably killed in the crash.
"It was unfathomable, it was something out of a movie", he told the newspaper.
The governor of Washington, Jay Inslee, thanked the Air National Guard from Washington and OR on Twitter "for scrambling jets to keep Washingtonians safe".