Jean Claude Pressac reproduced a letter (dated 29 January 1943) from SS-Hauptsturmführer (Captain) Karl Bischoff to SS-Oberführer (Sr. Colonel) Hans Kammler in his book Auschwitz: Technique and Operation of the Gas Chambers (The Beate Klarsfeld Foundation, New York, 1989, p. 432). The following is an English translation of that letter:
Except for some minor construction work, Krematorium II was finished by working with all our available forces day and night, despite inexpressible difficulties and freezing weather. The ovens were fired in the presence of the senior engineer Prüfer of the executing firm, Topf and Sons, Erfurt, and they are working faultlessly. The reinforced concrete ceiling of the morgue could not yet be eliminated due to the freezing weather. However, this is not significant, as the
gassing cellar can be used for this purpose.
Due to the railway car prohibition, the company Topf and Sons could not deliver the aeration and deaeration equipment at the time demanded by the Zentralbauleitung. After the aeration and deaeration equipment arrive, however, installation will begin immediately, so that presumably by February 20, 1943, it will be completely ready for operation.
Enclosed find a report of the inspecting engineer of the firm of Topf and Sons.