Video: here is what happened before stolen Seattle plane crashed

A "suicidal" mechanic stole an empty passenger plane from the Seattle-Tacoma airport late Friday, took it for a brief flight then crashed it in an incident officials said was unrelated to terrorism.

Two military F-15s were scrambled to chase the stolen plane, but local officials said the jets "were not involved in the crash."

Video taken by a bystander showed the passenger airplane making an unlikely upside-down aerial loop, then flying low over Puget Sound before crashing into the sparsely populated Ketron Island in the northwestern US state of Washington.

John Waldron, who took dramatic video of the stolen plane flying in a loop, told CNN that he was out for an evening stroll when he saw the two jet fighters following the turboprop airplane.

His first thought was that they were practicing for an air show. "So, I started to capture video, just because I thought it was, kind of bizarre," he told CNN.

Waldron said it seemed that the jets were chasing down the airplane. "I thought this is really odd. Kept the video rolling."

Then the passenger plane pilot "did a complete loop ... I couldn´t believe he recovered."

He estimated that the plane at its lowest point was no more "than 100 feet (30.5 meters) above the water."

Then the pilot "pulled -- pretty much straight up. And kind of at an angle. And almost stalled the aircraft. Somehow he got it leveled back off. And then made his way down toward the island."

Waldron said that he was prepared to "run and take cover." He briefly turned away, then turned back and saw the explosion as the plane crashed.

"Saw a bright, pinpoint area of flame. And the smoke. I thought, oh, my god. I think he just crashed."

A recording of the radio conversation between the pilot and the control tower shows the pilot oddly calm.

"Congratulations, you did it," the control tower tells the pilot, according to audio that aired on CNN. "Let´s turn around the air and land it and not hurt anybody on the ground."

"I don´t know, man," the pilot answers. "I don´t want to. I was kind of hoping that was going to be it, you know."