Overview: Whether it's the assassination of JFK or the events of 9/11, when national tragedies occur they trigger painful soul-searching. In both cases a national consensus emerged over time about the single gunman who shot JFK… and the reasons the towers collapsed on 9/11. But some still question the so-called ‘official version’ of history. They passionately believe in other – often radical – explanations. And they think there might be conspiracies to hide the real truth.