I'm not sure where the line is drawn. If Mac Wallace was directly involved as the fingerprint seems to indicate, then it would seem that Johnson was directly involved, as Wallace worked for him. Also, it was on Johnson's home turf, he was a direct, personal beneficiary of the assassination (as he became POTUS - the most powerful man in the world), he had foreknowledge of the event which he shared at least with his mistress (who apparently told many people in later years), and he was in a position to totally direct and cover up any "investigation".

So while I believe Johnson is far from alone in this....I think he's a good place to start. A thorough investigation of Johnson could be the thread that unravels. Unfortunately this big lie has so many participants that they all covered and cover for each other and the Big Lie has become institutionalized by the regime that has been in power since the coup. It is their Founding Myth and they will not easily let go of it.