I'm not convinced Diana was murdered. I'm not wholly convinced otherwise but I have thought about the logistics of murdering a person like Diana via a car crash, taking into account that her movements on that day were erratic and apparently subject to last minute changes. It has to be said that lovely though she was, she was quite erratic!
I would have thought such a murder would require some serious planning. For example, in the assassinaton of Kennedy, his whereabouts and route were a fairly long standing, pre-planned event and not subject to any changes of plan Kennedy himself might instigate. Such a certainty would enable anyone to be reasonably secure in an assassination attempt. A bullet to the head was a pretty sure-fire way of ensuring death, too.
To pre-suppose Diana was murdered would mean having a dedicated crew just sitting by in France waiting for her to visit. It would also mean the crew would be able to swing into action despite the many changes of plan instigated by Diana and Dodi themselves - apparently last-minute changes. It is said that they had intended to stay in the hotel that night but changed their minds, bringing Henri Paul in at Dodi's apparent insistence.
With regard to the ambulance and the length of time it took to get to the hospital - yes, there is something a little suspect about that. However, if you are ruthless, have your crew in place, why not get her to the hospital in record time and just adminster a little 'something' when she arrived? If you're heading up such a huge operation, that would have been perfectly achievable.
Why bother with a car crash at all? Why not induce a nice little virus to see her sadly fade away with, say, pnuemonia?
I've heard all the 'sacrificial' stories but I gather that any occult sacrifice has quite rigid timetables and requirements involved. Diana's erratic nature and movements leave much to be desired if the timing is to be achieved.
I don't totally dismiss the murder theory - but I do edge towards 'accident' based on the difficulties a car crash would have presented when there were certainly easier, far less suspicious ways to get rid of her.