so many rumours, so little facts 
That's what went over the wire in Germany (in short english translation):
- 13.3.1996: strong stomach pain -> hospital
- internal bleeding in the stomach
- successful operation to stop the bleeding
- doesn't wake up from a coma (he falls into during or after the operation)
- 14.3.1996: dies because of multiple organ failure
- autopsy: numerous, large liver tumors and acute poisioning supposedly from AS and amphetamines
I guess that's all the legit information available regarding his death.