We're trying to get accurate information about what is actually going on.
"It is highly fragmented", Debra Eckrote, the Western Pacific regional chief for the National Transportation Safety Board, said of the plane.
The plane crashed on Ketron Island, a small island in the Puget Sound that is home to about two dozen residents.
The plane had crashed near the southern tip of the island, its wings sheared off and the fuselage resting upside down.
She believes that once NTSB investigators reach the crash site they'll be able to find the cockpit voice recorder and the plane's data recorder. Russell "had access legitimately" to the plane, said Mike Ehl, director of aviation operations at the airport in the northwestern U.S. state of Washington, adding that "no security violations were committed".
"The greatest threat we have to aviation is the insider threat", Erroll Southers, a former Federal Bureau of Investigation agent and transportation security expert said. Southers is director of homegrown violent extremism studies at the University of Southern California.
"Yesterday's events will push us to learn what we can from this tragedy so that we can help prevent it from ever happening again, at our airline or any other", Brad Tilden, CEO of Alaska Air Group, said today during a news briefing at Seattle-Tacoma International Airport. Video has surfaced appearing to show the hijacker successfully executing the maneuver, some time before his fatal crash.More news: NFL finds 'defective' football in Steelers-Eagles game
The aircraft took off and began manoeuvering over Puget Sound.
"It may seem hard for those watching at home to believe, but Beebo was a warm, compassionate man", the statement said.
President Donald Trump was briefed and the White House praised authorities' quick response to the crisis. He's now at his New Jersey golf club. The man's condition after the crash wasn't immediately known.
In a statement released on Twitter, Sea-Tac Airport confirmed the reports of an "unauthorized takeoff".
Mr Russell, a ground service employee with Horizon Air, has not been officially named by authorities but his family have revealed his identity. He also says it's extremely lucky no one else was hurt. Got a few screws loose.
Air traffic controllers attempted to talk the man into landing at McChord field - but he refused.
In audio recordings of the incident posted on Broadcastify, the man can be heard talking to air traffic controllers as they try to guide him to land the plane.More news: Jordan Ayew joins Crystal Palace
The man later said that he was sorry.
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".
Treichel, who saw smoke rising from Ketron Island, didn't connect it to the plane until her son called to say the aircraft they had just seen had gone down. There were no passengers aboard. Jimmy Thomson, deputy editor of Canadian investigative news outlet The Narwhal, has compiled and transcribed portions of the air-traffic recording of the incident, and they provide a haunting glimpse into the moments before the plane crash.
"I've got a lot of people that care about me", he said at one point.
The sheriff said earlier that the employee was a airline mechanic, but the airline said he was a ground service agent.
"As far as taking off and navigating your way through SeaTac that's a big airport".More news: 'Mourinho at odds with the United board'
After "doing stunts in (the) air" - or being flown without proper skills - for about an hour, the plane crashed at Ketron Island, the sheriff's department said.
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