For some reason I remember when this disaster was announced in 1983 by the anchor on a Los Angeles news show: Breaking news. "An Air Korea 747 left Anchorage for Seoul. It never got there." The reason it never got there was that a Soviet interceptor had shot it down. At first the Russians denied it and then admitted that they had destroyed it when it entered restricted air space for the second time.
The investigation was turned over to the international agency that determined the KAL flight had never been on its correct heading but had drifted north, crossing into the USSR. The US Air Force, breaking its usual code of silence in these matters, informed the international committee that a secret USAF reconnaissance airplane had been slowly doing figure eights just off the Russian coast, and at one point the KAL flight had probably merged with the other's image on Soviet radar.
The conclusion of the committee was only that for some reason KAL was way off course. They couldn't determine the reason because the black boxes, which would have answered so many questions, was presumed to lie at the bottom of the sea. Uknown to anyone else, a Soviet submarine had recovered both boxes and kept them secret in a safe.
Sixteen years later, with the USSR in a state of near collapse, they turned over both boxes to the international committee. A KGB general personally handed them over to the committee chief and said it had bothered him for so many years to enter his office, look at the safe, and know that the boxes were inside but there was nothing he could do about it. The Russians contributed an air crash investigator to the international team. The French validated the authenticity of the tapes.
The ultimate conclusion was pilot error. The crew had set their autopilot for the wrong course and never noticed it because the instruments gave no warnings. The airliner crossed over a Soviet island then out again. When it entered restricted air space a second time, fighters were scrambled. The Soviet pilot fired warning shots but none were tracers so they went unnoticed. When the KAL flight began climbing, the fighters interpreted it as an evasive maneuver and followed routine procedures in shooting it down. The pilot of that fighter still believes it was an American spy plane he shot down. I don't blame him for wanting to believe it. The alternative is pretty horrible.
In any case it was an accident with unintended consequences for everyone involved. Instrumentation has been improved to help avoid such occurrences in the future.