http://www.pbs.org/wgbh/pages/frontl...nd-mexico-city
This is amazing, check out the footnotes, most of them are scans of correspondence between the most powerful men in Washington following the assassination.
They were literally freaking out about these CIA tape recordings of phone conversations an Oswald impersonator had with the Cuban and Russian consuls in Mexico only two months before Dallas that linked Oswald to this well known KGB assassin, they were scared shitless that if it got in the media that Oswald killed Kennedy while working for Kruschev and Castro that it would escalate into an all out nuclear war. So it was decided that the Warren Commission had to be pre-ordained to reach one conclusion, that Oswald acted alone.
This was right after the assassination, they had no idea if Oswald was or wasn't working for the Soviets - what I can't figure out is who was impersonating Oswald and why. The Russians and Castro surely if they had a part in Kennedy's murder didn't want it to get out and end up getting nuked by the Americans.