I have a simple conspiracy theory in which LBJ and the owner of the TSBD, Harold Byrd, conspire indirectly, to allow Oswald as much opportunity as possible to do the shooting.
The way I figure it, it is not inconceivable that LBJ,havng access to CIA, FBI info, became aware that the notorious defector to USSR, Lee Harvey Oswald, had returned to USA, and was working the TSBD, a building owned by a good friend, Harold Byrd, whom shared similar disdain for JFK as did LBJ.
So it would have been not too difficult to change the original planned route of JFK motorcade to turn on Elm st to make it easier for the "nut" Oswald whom the FBI KNEW was employed in TSBD (ie. Hosty file), which such info could have been found out by LBJ. So all LBJ really has to do, is make sure that his TSBD friend Harold Byrd keeps Oswald employed, and not secure TSBD building, and present the irresistible target, JFK , in proximity to "the nut", and probably had some psychological study that there was a better than 50% probability the "nut" would try to take a shot at JFK.
I believe there might have been a similar "roll the dice" probability plan for another "nut", Thomas Arthur Vallee, which COULD have been just as devastatingly effective, expect Vallee got intercepted via a tip off, was arrested with rifle and about 1000 rounds of ammo, in Chicago. That prompted the cancellation of a planned JFK motorcade visit to Chicago.