Exactly, but those agencies were involved in covering information but weren't necessarily involved in an assassination plot.
Not necessarily, but the KGB may have been.
IIRC, John M. Newman and Peter Dale Scott used to think (I think Scott still does) that evil, evil, evil James Angleton had somehow caused Kostikov's radioactive name to be mentioned by Soviet Embassy security officer Ivan Obyedkov to Oswald or an Oswald impersonator over a sure-to-be-taped-by-the-CIA phoneline on 10/1/63 so that the CIA and the FBI, in the interest of preventing Nuclear Armageddon, would be forced seven weeks later to cover up the CIA's hand in the assassination.