I wonder how much this is going to tingle your intellectual palate. According to a book by Brian Latell, the CIA's former national intelligence officer for Latin America, Fidel Castro knew about the impending assassination of John F Kennedy. Apparently, Oswald, having been refused a visa for Cuba, offered to prove his determination and loyalty to the Communist cause by offering to kill the President. Storming out of the embassy which had denied him the relevant bumf, he shouted: "I'm going to kill Kennedy for this!"

My answer to my opening question is: not very much, I bet. I think we long ago passed the My-Eyes-Glaze-Over moment when it comes to JFK's assassination. My own such moment came in 1991, a third of the way through a screening of Oliver Stone's sprawling, incoherent epic, JFK, when I finally stopped wondering, once and for all, who killed Kennedy, and started wondering instead what I was going to have for dinner, if I managed to make it through the remaining two hours of the film.

Unless, of course, you are a diehard conspiracy theorist, one of those for whom the assassination of the warmongering, hypocritical and mendacious US President has something approaching the status of a creation myth. The compound adjective most often used to describe the people obsessed with grassy knolls and so on is "swivel-eyed", but these men (and they are, invariably, men) actually betray a terrible fixity of vision in which they see only what they would like to see.

This kind of thing would be harmless, sort of, if these people hadn't, somewhere along the way, mutated into the kind of nut-jobs who think Obama isn't an American citizen, or is a Muslim, or that 9/11 was a put-up job (although they can't agree on whether the job was put up by the Pentagon, the President, the Jews, or Mickey Mouse). They also poison the well for those who have legitimate grounds for doubting official versions of events – the most interesting at the moment being, for my money, the ongoing doubts about the conviction for the Lockerbie bombing.

Anyway, back to Cuba, and Castro. (I prop my eyelids open with matchsticks as I write this.) Conspiracy theorists tend to twist the question "cui bono?" – "who benefits?" – at the expense of the principle of Occam's razor – "don't make explanations more complex than they have to be". The explanation for this latest tale lies in the words "book by Brian Latell" above. The mystery to me, and to many others, is not so much the possible Cuban involvement in the assassination, the evidence for which here is neither robust nor very significant, but in the eternal obsession with, and paranoid hostility to, communist Cuba, both of which have made American governments do their best, for over half a century, to immiserate its populace. Someone explain that to me and then maybe I'll be interested.