To concur with A-330, there were 2 KAL 747s flying from Anchorage to Souel that night. The first was KAL 007, the one that was shot down. The interesting facts were: the pilots on these 2 747s were Korean Airforce buddies; KAL 007 "developed" communication problems with the ground control in Alaska. It had to relay its position via the second 747. The information relayed and the actual flight path of the first 747 were different. It appeared that the second 747 was covering up the actual movement for the first one. And when KAL 007 was shot down, it had all of its navigation lights turned off.
This is a very complicated issue. The Soviets were not trigger-happy, blood-thirst monsters described by the US at the time of the incident. The KAL flight was not as innocent as a simple civilian flight. Many parties, like CIA, the US Airforce, Korean intellegence service, were probably involved in this incident.
The more sinister theory is that it's a covert operation planned by the CIA and US Airforce, with cooperation from Korean Airforce and KAL. The plot called for KAL 007 to invade the Soviet air space and cause the activation of their air defence system. The US RC-135 was to record the various radar and communication signals. Even if the 747 were intercepted and forced to land, KAL can just blame it on pilot error. The whole plot bet on the Russians won't shoot a civilian 747. KAL 007 flew a strange couse, changed its altitude and heading repeatedly. The fact that first few interceptions of KAL 007 were successfully evaded irrated Soviet air defence high command so much that the order was given to shoot the invader down at the first opportunity. The pilot finally caught up KAL 007 as the 747 was leaving the Soviet airspace. So the action was rather rushed. At the end, a fail safe plot failed and the 200 some passengers were the victims of the Cold War.