The Gagne book - "Thinking Critically...." - is especially good on the question of how exactly such a secret conspiracy could be planned in advance (no one said no?), executed (no one saw this being done?) and then covered up (no one blew the whistle?) when we have the problem of bureaucratic independence and inertia and rivalries. There is no such thing as "the government", not in the US. It's a series of agencies and departments and divisions filled with people of various backgrounds and views and interests.
Gagne makes this point: "Conspiracists are often silent on this matter [of how a bureaucracy could pull such a conspiracy off] but anyone who has studied the way institutional bureaucracies behave - with their particular chains of command, methods of internal communication, and bureaucratic trappings - might find it difficult to believe that a seamless conspiracy can be conduced by rival government agencies. It becomes even more questionable when we compound the number of agents and White House aides still faithful to Kennedy who maintained access to the evidence [and the investigation]."
Remember that LBJ kept *all* of JFK's people in his Administration, not only heading the departments and agencies but the Kennedy people, the Irish mafia, were kept onboard too. Why would he do this if he wanted to keep this quiet? It makes no sense.
So where was this plot planned out? Who led or initiated it? Where did they meet? How did they communicate? How were those who carried it out paid? Directed? Instructed? Where is the money trail? Where are the orders? I've read dozens of conspiracy books, more than I care to admit, and none of them lay this out. It's all "the conspiracy was off the books" replies if we get one at all.
We know the the civil service, the Administrative state, the bureaucracy of the US government cannot be controlled the way conspiracists say it was. It doesn't work that way. And multiple generations of people too? But in conspiracy world it doesn't work this way; "the government" is a single entity with the various agencies and departments and divisions - and all of the people in them - working together. It's a fantasy world they've created; not the real one.