Is that the same CIA that all liberals are so convinced made the  assessment that Trump 'colluded' with the Russians to win the election? You seem to want to change their role from villain to hero and back to villain at a whim.  I'm no fan of our 'intelligence' agencies as I think some have been involved with some shady characters in the past. 
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 Oswald immigrated to Russia, repudiated his US citizenship and  wrote a letter to Gus Hall in 1963, head of America's Communist Party, requesting membership. Oswald was a Communist. Kennedy was as anti-Communist as you can get. 
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Nixon was bitter?  Logically, he would have had Pat Brown done in. Unlike Nixon, Johnson had motive and opportunity. Which is why he didn't pursue the Communist connection as it would have meant war with Russia and anyway,  he was now the President. I think he may have 'known' about the plot to kill Kennedy, but because  it worked in 'his favor', he kept quiet.
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Yes, by all means the files should to be released..