Uhm, if we had a tape of Lee Harvey Oswald from before the assassination talking to a camera saying how he was going to go about assassinating JFK and shows how it was perfectly feasible for him to do so, I would suggest that this would be pretty convincing proof that he did it, would you not.

If one then said "no, he is part of the conspiracy", I could only shake my head at how loony that person is, in that they have to create a far more complicated theory when the evidence makes it all too easy to understand.