Airport officials said the airline employee had "conducted an unauthorised takeoff without passengers".
Witnesses reported seeing the plane being chased by military aircraft before it crashed.
Late yesterday's full stop at Seattle's Sea-Tac airport turned out to have a freakish and ultimately tragic reason. Pacific time, officials said. "We might get lucky and find them pretty quick - we may be out there all day".
At one point, Richard apologizes to those he loves for his actions. "It's going to disappoint them to hear that I did this", he said. "I never really knew it until now".
"They don't have any of that stuff", the air-traffic controller said. It did not elaborate.
"I've got a lot of people that care about me". We're trying to get accurate information about what is actually going on. "But could you start a left-hand turn, please?" There were no other people on board, and the man piloting the plane has not been recovered. "I'm down to 2,100 (pounds)", he is heard saying.
"FAA air traffic controllers communicated with the individual who was flying the aircraft to try to help him land safely".
The man responds: "Awwww-right ... dammit". I don't know! I don't want to.
The FBI is investigating the freakish incident in conjunction with the National Transportation Safety Board and local law enforcement.
The 29-year-old ground service agent, whose name was not released, hijacked a 76-seat Q400 aircraft belonging to Alaska Airlines' regional carrier Horizon around 7:30 p.m.
"I want to thank the Air National Guard from Washington and OR for scrambling jets to keep Washingtonians safe", Washington Governor Jay Inslee tweeted. It crashed on the south of Ketron Island, near a military facility. The jets were armed but did not open fire, North American Aerospace Defense Command spokesman Cameron Hillier said by phone.
Two F-15 fighter jets scrambled from Portland "minutes later" to intercept it, according to Pierce County Sheriff's Office.
Mr Russell's family said in the statement that the recordings showed he wasn't planning to harm others. He didn't hear the crash, but saw smoke.
Alaska Airlines also confirmed the 27-year-old had been "background checked" and had worked a shift at the airport prior to stealing the plane. The Horizon airplane was followed by two F15 jets which attempted to escort the stolen aircraft back to Sea-Tac.
"I thought they were practicing for an air show", he said.
Beck described the flight as being an hour long before the crash on Ketron Island. The plane was "highly fragmented and the wings are off", she said.
"We are going to be thorough, which means taking the time needed to scour the area, delve into the background of the individual believed responsible, and review every aspect of this incident with all appropriate public & private partners", the Federal Bureau of Investigation said in a statement.
It wasn't clear what training, if any, the man had as a pilot.
"Safety is our number one goal", Alaska Airlines chief executive Brad Tilden said. "They're not as easy to fly as, say, a Cessna 150, so I don't know how he achieved the experience he did", the CEO said.
"So, (he) had some knowledge but clearly wasn't a commercial pilot". Preliminary info is that a mechanic from unknown airlines stole plane.
Alaska Airlines said: 'We are aware of an incident involving an unauthorized take-off of a Horizon Air Q400.