Personally I have little time for so-called conspiracy theories, least of all for those surrounding lifestyle-deaths such as Monroe and Diana. Boring. However, there is, just occasionally, a rather too-easy willingness to cry "conspiracy theory" when one suspects the attempted covering-up of a miscarriage of justice. I've always believed this to be the case with the Lockerbie bombing. One of the first things that happened after the crash was that the scene, containing vital evidence, was violated, not just by well-meaning locals but, far more significantly, by swarms of unidentified Americans who were spiriting away that evidence. Read about it here:

http://www.lrb.co.uk/v31/n18/gareth-peirce/the-framing-of-al-megrahi

And don't get me started on the testimony of the demented shopkeeper in Malta which was such a vital part of the prosecution case. At least he was well paid by the yanks.