The sheriff's office also said that the F-15s arrived minutes after the plane was stolen and kept the aircraft "out of harm's way and people on ground safe".
Erroll Southers, a former Federal Bureau of Investigation agent and transportation security expert, told AP "the greatest threat we have to aviation is the insider threat". We know who he is.
The 29-year-old man identified as "Rich" or "Richard" flew out of the Seattle-Tacoma airport with a twin engine, 76-seat turboprop Bombardier Q400 belonging to Horizon Air at around 8pm local time Friday (10am Saturday Thailand time).
Pierce County Sheriff's spokesman Ed Troyer told the Bellingham Herald that information was preliminary regarding the developing incident.
A Horizon Air airplane was stolen from SeaTac Airport on August 10, 2018 and crashed on Ketron Island where it sparked a fire. There were no passengers aboard. It crashed near Ketron Island in Pierce County, the airlinetweeted, adding that "we believe" nobody besides the man was on board.
Those employees direct aircraft for take-off and gate approach and de-ice planes.
"Safety is our No. 1 goal", said Brad Tilden, CEO of Alaska Airlines. Without confirming anything, a stolen aircraft would be a security issue. Horizon Air is part of Alaska Air Group and flies shorter routes throughout the West in the United States.
Local media citing sources at Joint Base Lewis-McChord (JBLM) air force base said one or more F-15 fighter planes contacted the rogue aircraft and it crashed soon afterwards.
Sheriff Paul A. Pastor said at the press conference that there was no sign that it was a terrorist attack.
In audio recordings posted on Broadcastify, the man can be heard talking to air traffic controllers as they try to guide him to land the plane.
The controller replies: "If you could, you just want to keep that plane right over the water".
Later on the pilot says: "I've got a lot of people that care about me. It's going to disappoint them to hear that I did this", he said.
While in the air, Russell joked for almost 20 minutes with the air traffic control agent, but admitted he had "a few screws loose" and called himself "just a broken guy".
SeaTac Airport was temporarily grounded amid a security threat. After flying around an unpredictable path, the plane crashed at a nearby island.
A fire sparked by the Friday night crash "is pretty much out", Eckrote added.
"It is highly fragmented", she said of the plane. I think I might mess something up there too. Investigators are trying to find how he got on the plane.
They called a second alarm, Adams said, to get more crews out to the island.
On Saturday morning, White House Press Secretary Sarah Sanders told media that PresidentDonald Trump was briefed on the incident and is now "monitoring the situation" in Seattle.
We would like to thank the authorities who have been both helpful and respectful, Alaskaair for their resources, the community, his friends and his family for their incredible support and compassion, and Jesus whose steadfast love endures.
Alaska Airlines said no structures on the ground were damaged. Authorities said he took the airplane from the maintenance area and used a push back tractor to rotate it 180 degrees before takeoff.
"It was unfathomable, it was something out of a movie", King told the Times.
The FAA ordered the airport to a "groundstop" during the incident and NORAD launched two F-15 fighter jets to follow the plane.