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.
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".
Who was Richard Russell?
The airline worker, whose nickname was Beebo, has not yet been formally named as the pilot of the plane but he has been identified as such by his family and by US media.
In a statement, his family said they were "stunned and heartbroken".
"It may seem difficult for those watching at home to believe, but Beebo was a warm, compassionate man," the statement said.
"He was a faithful husband, a loving son and a good friend."
According to an online blog, Mr Russell lived in Sumner, Washington. He was born in Key West, Florida, and moved to Wasilla, Alaska, when he was seven years old.
His profile tells of how he met his wife in Oregon in 2010 and says they ran a bakery together there for three years before moving to Washington to be closer to her family.
Mr Russell was active in the local Christian youth ministry, often working with troubled children.
He also writes about his job with Horizon Airlines, saying he is "able to fly to Alaska at my leisure".
"In this season of life we enjoy exploring as much as possible, whether it's a day (or so) trip to one of Alaska Airline's destinations, or visiting a new area of Washington," the blog post, apparently written two years ago, says.
A former airline colleague of Mr 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."
What have officials said?
Mike Ehl, director of aviation operations at the airport, said the employee "had access legitimately" to the plane and that "no security violations were committed".
Alaska Airlines CEO Brad Tilden said the worker 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 he 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.
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 employee 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.
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.
Some dude stole a plane from #Seatac (Allegedly), did a loop-the-loop, ALMOST crashed into #ChambersBay, then crossed in front of our party, chased by fighter jets and subsequently crashed. Weird times. pic.twitter.com/Ra4LcIhwfU— bmbdgty (@drbmbdgty) August 11, 2018
Officials say they lost contact with the plane at 20:47 local time, more than an hour after it left the airport.
What did the pilot say to air traffic control?
Richard Russell's messages vary from options for landing, to apologies for what he is doing to the often bizarre.
The controllers suggest he needs some help flying the plane, to which he replies:
- "Nah, I mean, I don't need that much help; I've played some video games before."
But he also shows a limited knowledge of operations, acknowledging that the amount of fuel used on take-off was quite a lot more than he expected and that some instructions to him were "mumbo jumbo".
Advised that he try to land at the US Air Force base at McChord Field, he says:
- "Aw man, those guys would rough me up if I tried landing there... Oh, they've probably got anti-aircraft."
The controller asks for a left turn, receiving the reply:
- "This is probably jail time for life, huh? Well I hope it would be for a guy like me."
Among the more odd exchanges, Mr Russell discusses:
- The co-ordinates for an orca carrying her dead calf on her back which featured in the news last week
- Looking at the view and possibly going to look at the Olympic Mountains in Washington state
- Whether or not Alaska Airlines would give him a job after a successful landing
However, there are also indications that Mr Russell might not have been expecting to land safely. He talks of doing a barrel roll and "calling it a night" by going "nose down".
When asked to land he says: "I don't know, man. I don't want to. I was kind of hoping that was going to be it, you know."
He also says: "I've got a lot of people that care about me. It's going to disappoint them to hear that I did this.
"I would like to apologise to each and every one of them. Just a broken guy, got a few screws loose, I guess. Never really knew it, until now."