The story of John Garrett Underhill Jr. is not necessarily a new revelation, but it’s certainly a great place for noobs to start.
Underhill was Military Intelligence during WW2, had connections to the CIA, and post-Kennedy assassination he claimed the CIA were responsible.
Underhill claimed the CIA were running a gun/drug trafficking operation, Kennedy found out about it, and the CIA took out Kennedy before he could “blow the whistle”.
Six months later, Underhill was found dead with a bullet wound behind his left ear, in what was ruled a suicide.
There’s not going to be an official CIA document that says “we killed JFK”, but there will be a large accumulation of evidence that suggests that conclusion.