Cargo one , final try : there are internationally agreed procedures to intercept civil aircraft , USSR (Russia) signed them . In case of KAL 007 they were not followed and someone high up in the Soviet military gave the order to shoot down a 747 without proper attempt of identification , call on 121,5, forced to land, firing tracers in front , etc...
Initially ( i.e immediately after the accident in 83 ) they said they mistaken it for a USAF RC135, but the R/T and telephone transcripts released in 1993 showed that the Sukoi pilot first flew alongside the 747 knew it was a civilian 747, reported lights ,etc.. but none of the usual interception rules were followed.
And as cessnaxpilot pointed out , there was nothing out there, and they were heading out of Russian airspace when they decided to shoot it down before it entered international waters again .
The Su15 pilot that shot it down gave an interview in 1991 here is an extract what he said :
In a 1991 interview with Zwestia Major Gennadiy Osipovich, pilot of the Su-15 interceptor that shot the 747 down, spoke about his recollections of the events leading up to the shootdown. Contrary to official Soviet statements at the time, he recalled telling ground controllers that there were "blinking lights" .He continued, saying "I saw two rows of windows and knew that this was a Boeing. I knew this was a civilian plane. But for me this meant nothing. It is easy to turn a civilian type of plane into one for military use."[size=8333px] [/size]: "I did not tell the ground that it was a Boeing-type plane; they did not ask me." Later we began to lie about small details: the plane was supposedly flying without running lights or strobe light, that tracer bullets were fired, or that I had radio contact with them on the emergency frequency 121,5, all not true. [size=8333px] [/size]