A man who stole an empty passenger plane from Seattle airport and then crashed it was an airline worker with full credentials, authorities say.
The 29-year-old had worked for Horizon Air for more than three years, towing and tidying aircraft and loading bags.
The man, named by US media as Richard Russell, took off late on Friday, forcing the airport to close while two fighter jets gave chase.
After making "incredible manoeuvres", he crashed the plane and was killed.
The flight lasted 90 minutes and the crash site is on Ketron Island, a sparsely populated area in Puget Sound.
"At this time, we believe he was the only one in the aircraft but of course, we haven't confirmed that at the crash site," said Jay Tabb, chief of the FBI's Seattle division.
A former airline colleague of Russell described him as a "quiet guy".
"He was well liked by the other workers," Rick Christenson told The Seattle Times. "I feel really bad for Richard and for his family. I hope they can make it through this."
Transcripts of his conversation with air traffic control reveal a man who appears surprised about his feat, who is unclear as to the full operations of the plane, who has no intention to hurt anyone and who ultimately apologises to his loved ones, saying he is "just a broken guy".
What are the latest developments?
Airline and airport officials gave a press briefing on Saturday morning in Seattle.
Mike Ehl, director of aviation operations at the airport, said the man "had access legitimately" to the plane and that "no security violations were committed".
Alaska Airlines CEO Brad Tilden said he had been "background checked".
"He worked his shift yesterday and we believe he was in uniform," he added.
Mr Tilden said planes do not have door or ignition keys, and that other airport security measures keep them safe.
Gary Beck, CEO of Horizon Air, said that "to our knowledge, he didn't have a pilot's licence" and that he had no idea how the man had gained the skills to fly such a "complex machine".
FBI spokeswoman Ayn S Dietrich-Williams said agents were working with the transportation safety board and other groups to process the scene of the crash on Ketron Island.
"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," she told reporters.
What happened exactly?
The 76-seat, twin-engine turboprop Bombardier Q400, belonging to Horizon Air, took off from Seattle-Tacoma International Airport at 19:32 local time (02:32 GMT).
Officials say the man used a pushback tractor to first manoeuvre the plane 180 degrees from a maintenance location into the correct position for take-off.
After take-off he performed at least one dramatic roll, pulling the aircraft up just metres from the water before gaining altitude again.
The North American Aerospace Defense Command (Norad) issued a statement saying that two F15 fighter jets were launched from Portland to intercept. A number of videos showed them following the passenger plane, which was flying in an erratic manner.
Norad said the F15s were "working to redirect the aircraft out over the Pacific Ocean when it crashed on the southern tip of Ketron island", about 30 miles (48km) south of the airport.
"Norad fighters did not fire upon the aircraft," it said.
Officials say they lost contact with the plane at 20:47 local time, more than an hour after it left the airport.