JFK: The CIA, Vietnam and the Plot to Assassinate John F. Kennedy
by L. Fletcher Prouty
I find Col. Prouty quite convincing. He was a high-level officer in the military and the CIA, working in the field from late WWII and then in the Pentagon, where he briefed the President and the Joint Chiefs, until he resigned shortly after JFK's death. His commentary is not so much about the assassination, although that is well covered at the end of the book, as about the history of the Cold War, especially Vietnam and Prouty's analysis of the Pentagon Papers. I found some of the details shocking, e.g. there was an enormous U.S. stockpile of U.S. arms on Okinawa in preparation for the invasion of Japan in 1945; when the A-bomb made the invasion unnecessary, the arms were split and given away to North Vietnam (Ho Chi Minh) and North Korea by the military-industrial complex that President Eisenhower warned about, because they (the M-I C) profit from continuing warfare.
Call me a conspiracy nut if you like. It's true I've read quite a few books on those events. If you're convinced Oswald was the lone gunman, I would suggest you avoid this one, at risk of having your ideas severely shaken up. The only source of doubt I have about him is his association with the Church of Scientology (perhaps the only organization that dared publish his work?).
This book was originally published in 1997, and used as one of the principal sources for Oliver Stone's movie (in which Donald Sutherland as "Mr. X" portrayed him. It was updated in 2009 with a preface by Oliver Stone. (Prouty died in 2001.)