The famous Belgian war hero Albert Guérisse testified under his alias Patrick A. O'Leary about witnessing a flaming chimney whilst held prisoner at Natzweiler-Struthof. He testified at the post-war trial on May 30, 1946.
This surely deserves a mention, as it's the only example that I know, of a flaming crematorium chimney being thoroughly discussed at one of the victor's trials :
Major Hunt: (prosecutor) Where are you stationed at the moment?:
Lieut.-Commander O'Leary: London.
Where were you in September, 1944?
I was a prisoner in Natzweiler Concentration Camp.
Do you remember seeing any women in the camp?
I remember having seen four women at the end of July, 1944, in Natzweiler Concentration Camp.
Can you tell the Court the circumstances under which you saw them?
I saw the four women, at least one of them, in the cell where she had been gaoled.
Did you see them arrive?
Yes, I saw them walking down the camp on their way to the cells.
Were you able to speak to one or any of them?
Yes, I spoke to one of them.
Tell the Court what transpired at this conversation?
At the end of the afternoon of the day the women arrived, a Dutch doctor who was in charge of the block which was next to mine told me that I would be able to speak to one of the women who had been gaoled in the hut which was opposite his. So at about seven o'clock in the evening I went to the hut where the Dutchman lived, went to the window, whistled, and saw a woman appear at a window in her cell. I told her, "I am a British officer." I asked her, "Who are you?" She said, "I am British." She said, "I am British." She wished me the best of luck and I wanted to keep on talking but unfortunately the S.S. appeared, a guard.
You mean that owing to the presence of guards you were unable to continue the conversation?
Do you recall further events of that particular day?
Later in the evening, at about nine o'clock, an order was given that none of the prisoners in the camp was allowed out of his hut and that nobody was allowed to be seen at the windows of the huts ; so we knew that something very unusual was going to happen.
Had that order been issued previously or was it subsequently?
As far as I know it was the first time such an order was issued at the camp.
Did you subsequently on that evening have any opportunity to see any of these women again?
Yes, when the night came I went to the window of my hut and I saw one woman coming out of the gaol and going to the crematorium. With her were S.S. men with torches.
Were you able to recognize any of the guards?
No, but a little before nine o'clock, a little before this took place, I saw Rohde, who was with the former doctor of the camp and this doctor was in civilian clothes; I saw them both going to the crematorium.
Were they alone when they were proceeding to the crematorium?
Did you see anybody else going to the crematorium that night?
I saw S.S. officers going to the crematorium and S.S. guards.
You were describing just now how you saw a woman under guard moving in the direction of the crematorium. Did you see anything else of this sort?
I saw first the woman with the S.S. men going to the crematorium. A little later from my window I could watch flames coming out of the chimney of the crematorium.
Was this a usual occurrence to observe these flames?
Yes. When the door of the oven was opened in the crematorium the flames used to come out of the chimney.
Did you see only one woman or more than one woman proceeding to the crematorium?
1 saw the four women going to the crematorium but one after another.
At what intervals did they go one after another; or was there an interval between each one?
Well, they went one after the other — two or three minutes — one went, and two or three minutes later another went.
This question of the flames coming out of the chimney ; was that momentarily only, or was it continuously appearing?
I did not know when that appeared what it meant, but the next morning the morning the German prisoner in charge of the crematorium explained to me that each time the door of the oven was opened the flames came out of the chimney and that meant a body had been put in the crematorium.
Do you remember how many times you saw this that night—that is the flames?
I saw the flames four times.
Do you remember or would you recognize the prisoner who told you about this procedure?
I think so.
Do you recognize him here?
Yes, the little man there with dark hair (witness identified Berg).
War Crimes Trials Volume 5: The Natzweiler Trial , London: Hodge & Co., 1949, pp. 75-76.