Posner has updated his book in various editions.
There were many small disjointed cover-ups surrounding the assassination, the SS, the CIA, the FBI, Dallas police, Texas Rangers, etc. each scrambled to not be embarassed by not being vigilant enough when they should have been. It’s not any more than that.
The thing about conspiracy obsession is that if experts like Posner and Bugliosi debunk a conspiracy, somehow a new deeper conspiracy is invented to explain why they are wrong. It never ends.
Extraordinary claims require extraordinary PROOF and there is none here.
If that was the case, why would anyone cover up anything about it today?
I agree, if one goes into Conspiracies, why not say the Communists did it? It would also give reason to worry about is released.
“Why the Communist Killed Kennedy”, one can make the same kind of case as those saying Cuban Exiles, etc. did it.
http://americasurvival.org/2017/10/why-the-communists-killed-kennedy.html#axzz4wQkpuQdK