The Warren Commission says that Lee Harvey Oswald acted alone in the murder of President John F. Kennedy in Dallas, Texas, on November 22, 1963. I say it doesn't add up, and the main reason I say that is because it requires acceptance of too many coincidences. Follow me past the break, and I'll lay them out for you.
By chance the usual and customary precautions for a motorcade -- all windows closed, and extra security on the streets, watching the windows, not the parade -- were not followed in Dallas. The motorcade route by chance went past a building where a man worked who by chance claimed to be a Marxist and had tried to defect to Russia. By chance the FBI considered him a harmless crank and kept poor surveillance on him. By chance he was also at a crisis point in his marriage and was itching to hit out. By chance he was an expert marksman and owned a rifle which he'd bought under an assumed name. When he fired on the motorcade, many people looked up and saw his rifle; some even remember seeing him holding it before the shooting and thought he was Secret Service. But by chance, no real Secret Service agent or police officer saw him after the shooting; by chance none of these trained professionals fired back. After Oswald's capture, by chance security was lax enough (on a presidential assassin!) that Jack Ruby got through it and shot him -- thus killing the whole truth along with him.
Now that is a fantastic, incredible set of coincidences. The odds against any two such incidents coinciding must have been phenomenal, let alone four or six or ten. If I read that story in a book, I wouldn't be able to believe in it -- it's too contrived; too unlikely. And yet the Warren Commission presents it as non-fiction and expects us to believe it. Well, as Daffy used to say (or spray), "Not this little black duck!"
Well then (you might well ask), who did shoot President Kennedy? How many shooters; where were they? Who planned it; who produced, directed, stage-managed? And why?
All I can offer are hypotheses that make the most sense to me, given the particulars of the situation. At least one shooter besides Oswald, probably on the grassy knoll. The CIA appears to be involved at every step of the way, from the Bay of Pigs to the attempts on Castro's life to the Russian exile support group that "handled" Lee and Marina Oswald when they first arrived in Texas. Two or three of the Secret Service had to be involved. Motive? Pick one. JFK had pissed off the Texas oil barons, the wealthy Cuban exile community in Miami, the Mafia, and the military-industrial complex. The CIA had ties to all of them -- and they also had their own personal bone to pick with Kennedy, since he'd clipped their wings so severely after the Bay of Pigs.
In my opinion the movie "JFK" is way over the top, and it brings in people whom I believe had nothing to do with the assassination. However, there's one scene that always gives me chills. It's the one where the ex-spook played by Donald Sutherland is telling Garrison, played by Kevin Costner, all the anomalous happenings that took place on the day of the assassination and the days leading up to it. Every word he says in that scene is true (according to what I have read), and it explains that the many, many coincidences weren't coincidences at all: each one happened by design. People didn't just suddenly, inexplicably not do their jobs correctly; they were ordered or coerced or paid not to. And as horrible as that may sound, it also makes sense. It makes the story believable. It's the simplest explanation and thus, according to Occam's Razor, the most likely.