After consultation with the Attorney General of the GDR, however, it was ascertained that Oberhauser had only served a portion (eight years) of his fifteen-year prison sentence in the GDR and that he had not been convicted in Magdeburg of his role at Belzec extermination camp, but for his involvement in the Action T4 euthanasia programme.
Before the war, there were 300,000 Jews living in the region, which became the site of the Majdanek and Belzec concentration camps as well as several labour camps (Trawniki, Poniatowa, Budzyn, Puławy, Zamość, Biała Podlaska, and the Lublin work camps Lindenstraße 7 (Lipowa Street), Flugplatz, and Sportplatz) which produced military supplies for the Wehrmacht and Luftwaffe).
After 1939, and the demonstration or "proof of concept" that the firm could design an incinerator which would handle large numbers of corpses, Nazi officials further contracted Topf and Sons to provide similar incineration furnaces for the Belzec, Dachau, Mauthausen, Gusen Concentration Camps, and larger industrial incinerators especcialy designed for Auschwitz Concentration Camp.
Pfannenstiel was with Kurt Gerstein in Belzec concentration camp in August 1942 during which he witnessed the botched gassing of Jews from Lwów, an episode which Gerstein included in the subsequently named Gerstein Report and which is partly corroborated in the report of Wehrmacht NCO Wilhelm Cornides.