I want to elaborate on my earlier comment to Steve about the CIA going rogue for more clarity:
Do I believe it's plausible that plotting JFK's assassination was ever official CIA policy? No. I don't think the CIA director ordered a hit on Kennedy.
At worst, I find it plausible that some individual CIA officers and contractors went rogue against Kennedy. Which is close to the HSCA's conclusion.
A year or so ago, I listened to a podcast that featured legendary CIA officer, Felix Rodriguez. In explaining the differences between the CIA today and the 1960s, he basically said, back then, they would do unethical stuff and let the CIA's lawyers clean it up afterwards. In contrast, today, the CIA officers talk to lawyers before proceeding with operations.
Under the context of the CIA's earlier years when there were agents who did some things that they had to hide from the President and even the CIA director, I don't find it implausible that some CIA operatives could've been involved in a plot against JFK. Recently declassified files have confirmed that upper levels of the CIA didn't know much about some of James Angelton's most secret operations. He hid stuff from everyone, including people who worked closely with him. And it's well known that CIA officers hid stuff from John McCone, Kennedy's pick for CIA director, after Dulles was fired.
If all of that is true or even suspected of being true, it would be in the interest of the CIA as an agency to cover up any potential links to Oswald or the Kennedy assassination rather than come clean about the possible involvement of their guys.
It's that context which explains why the CIA didn't disclose to the HSCA that George Joannides ran the DRE at the time when LHO was engaging with their operations in New Orleans. And why James Angelton lied under oath to the HSCA about his interest in Oswald prior to the assassination.