the logistics would be fairly easy to sort out, given the resources available to the 'ptb', or whatever you wish to call them. multiple scenarios would be planned for, including all manner of variables, with 'appropriate' responses attched to each scenario. to reduce variables, events would be manipulated externaly as much as possible. if person A does action B, then response B would be used. if something is changed at the last moment, a prearranged contingency is activted. there are only so many variables involved with a high profile person such as the princess, no matter how randomly she may have acted.
remeber, high profile targets must be removed in a high profile way, so as to maximise the impact and effectivness of the action, be it political, occult, financial, religious, social etc etc. if diana had died of a mytery illness, where is the shock value? a spectacular car crash is much more productive. the seemingly untidy handling of the action merely serves to strengthen the impact. people are still focused on trying to figure out what exactly happened aren't they?
just my two cents worth
