Honestly? I think that what happened is some weird fucker who was on the radar of at least two TLA agencies was local when someone shot the president and both of those agencies immediately went "we can never let anyone found out how utterly incompetent we are, we need to cause enough smoke, dust and bullshit that even if someone reaches the right conclusion about what happened everyone else will have plenty of reason to disbelieve it." I think they executed the easiest coverup in the world because part of their goal was to make sure everyone knew there was a coverup, just not what they were covering up or on behalf of whom. Was Oswald a patsy? Maybe. If he wasn't he made a lot of really bad decisions in the moment leading up to the first shot being fired, then redeemed himself with some shooting that was so heroically accurate and well-drilled that it bordered on impossible with the gear and positioning he had. Did a bunch of people panic and start trying to ratfuck the investigation? Absolutely. Will they wait until everyone involved's great grandchildren are in the dirt before they tell us one honest word about this? Also yes.

Because the government classifies things when they're simply embarrassing. It doesn't need to rise to "national security threat" for the USA to feel the need to quash the ability of citizenry to talk about it. Even if it's not all that bad and simply embarrassing. They are way too cavalier about using classification powers because they don't want their dirty laundry aired.

What's left to release is probably a lot less exciting than people think.