While I have no "official" sources, I have read that EPO was part of his final condition. Something about the EPO increased red blood cell count, along with extreme dehydration, causing his blood to sludge, and his liver dissolving or something of the like.
Here is an excerpt from an article titled "Dying to be Arnie" taken from here:
http://www.ergogenics.org/arn6.html
The stomach pains had begun some months before Andi went to Columbus, Ohio, for the 1996 Arnold Classic. At first it was just more pain, and pain was the currency of muscle. Andi paid it little heed. It dug in and nestled down with all the other pain: the agonies of training, the banal deprivations of dieting down, the pulls, nicks, strains, jags and twists of the gym. But it kept coming back and its payload was different. A connoisseur of pain like Andi would soon have been able to tell. He would have been able to recognise it and rank it as something special in the pain game, something more exotic than the stuff he usually bore. He began to mention it to friends at the gym. He tried some health cures that would strengthen his stomach lining. Perhaps if Andi had quit training then, if he had turned away from the withering deprivations of another round of competition and stopped juicing he might have survived. Instead, the boy from Pack made himself ready to compete in front of the boy from Thal, in front of his hero.
After his sixth place at the Arnold Classic on 2 March 1996, Andi's mood remained low. 'Man, why don't you laugh?' a German official had said. 'You're the best white guy behind five Negroes.' Andi was never going to laugh at that. Best white guy. Best German speaker. All of the pain and deprivation, all of the gym seminars and pain-filled nights for those worthless epithets.
On the morning of 13 March, Andi's stomach pains became intense. His gut was swollen and hard. His bill had come in. He was fairly sure that this time he couldn't meet it. The debt was too big. The agony grew.
He was taken to hospital. Doctors there diagnosed the bleed, but could not prevent it continuing. He was transferred to the University Clinic. At 7pm, surgeons decided to operate to stop the bleeding inside Andi's stomach. Andi came through the operation, but his problems had multiplied catastrophically. His blood was viscous and slow-moving. His potassium levels were excessively high. He had been dehydrated by the diuretics he used in the days before his last competitions. His liver was melting. A post-mortem would find that it had dissolved almost completely. Andi's body went into shock. After his liver failed, his kidneys did too. He was offered a blood transfusion, but it was too late. Andi's heart held out for a while - he had always had a big heart - but by morning Munzer had joined the ranks of the bodybuilding dead.
Here's a more detailed look into what his regime looked like as posted by Deacon:
https://thinksteroids.com/community/posts/293631