Horrified Kurt Gerstein decided to sabotage or at least slow down the Holocaust, to tell the world about the Nazi genocide:

"I prayed with them and cried out to my God and theirs. How glad I should have been to go into the gas chambers with them! How gladly I should have died the same death as theirs!

Then an SS officer in uniform would have been found in the gas chambers. People would have believed it was an accident and the story would have been buried and forgotten. But I could not do this yet. I felt I must not succumb to the temptation to die with these people. I now knew a great deal about these murders."

On the night of August 20-21, 1942, on his way back to Germany, Kurt Gerstein travelled by train from Warsaw to Berlin and accidently encountered the Secretary to the Swedish Legation in Berlin, Baron Göran von Otter.

In his superbly written book A Spy For God Pierre Joffroy tells how von Otter had been unable to get a sleeper and stayed in the corridor: "There was an officer in SS uniform who seemed to be having the same trouble. He kept glancing at me, but I got the impression that it was from personal interest, not because he had me under surveillance."

Less than an hour from Warsaw, the train stopped at a station and von Otter got down to get a breath of air: "He followed me on to the platform and asked if I would give him a light. I produced a box of matches of the kind that were issued to us, with the words Swedish Consulate printed on it, and while I was lighting his cigarette he murmured: I want to talk to you. May I come and see you in Berlin?"

With beads of sweat on his forehead and tears in his eyes Kurt Gerstein suddenly burst out: Yesterday I saw something appalling. Von Otter asked him what he meant, but now Gerstein was weeping and could only repeat: ... something appalling.

"Is it to do with the Jews?" von Otter asked. "I don't think he answered. We couldn't go on talking on the platform. We got back into the train and sat on the floor at the end of the corridor. He had got himself under control ... The train was blacked out and the corridor was very badly lit, but there was enough light for me to read his identity papers and instructions."

In a feverish conversation lasting 10 hours, Kurt Gerstein poured out the whole story, crying and smoking incessantly. He related all he had just seen to the Swedish diplomat and begged him to tell the Swedish government about the atrocities in the camps.

Von Otter later recalled: "He gave me full details, names of the people carrying out the operation, and those higher up who were responsible ... he told me how he had come to be involved. His sister, or some other close relative, had died in a mental home, in circumstances that seemed to him so suspicious that he resolved to investigate further. Hence his entry into the SS."

Kurt Gerstein desperately urged von Otter to make the Holocaust known to the Allies and the outside world. His idea was that the Allied air forces, acting on Swedish information, should drop millions of leaflets over Germany, telling the German people what was going on, so that then they would rebel against Hitler.

Von Otter later described the encounter: "It was hard to get Gerstein to keep his voice down. We stood there together, all night. And again and again, Gerstein kept on recalling what he had seen. He sobbed and hid his face in his hands. From the very beginning as Gerstein described the atrocities, weeping and broken hearted, I had no doubt as to the sincerity of his humanitarian intentions."

Göran von Otter filed a report to his own government, which found it, as did other neutrals, too bizarre for credibility, and it was never acted on. But Gerstein maintained contact with the Swedish embassy in Berlin and kept it informed of the extermination operations.