If, indeed, LHO was the lone assassin, etc, then why would the CIA keep thousands of pages still classified for years after it was supposed to be declassified?
End of story. They either did it themselves, arranged it to be done by others, or know who did it in a way that conflicts with the official narrative. In any of these cases, criminal actions or criminal concealment of actions definitely occurred.
Yep, I vote for #3.