The facts are, Nikita Khrushchev was humiliated by the outcome of the Cuban missile crisis. Oswald lived in USSR, came back to the US to discover that nobody really cares, and was eager to gain some sort of celebrity status. He was also nuts. Could the Soviet Union know about his plans and give him some help? Possibly. This would also explain the secrecy around the documents. Any decisive knowledge that a foreign country had a major role in an assassination of an American president would lead to a war between two nuclear nations. We probably wouldn't know until the last documents are declassified.