Research into the wartime civil registries of one of the civil registry offices in Upper Silesias (Poland) discovered many records that corresponded to deaths of inmates from the "Reichsautobahnlager Annaburg" and "Zwangsarbeitslager Niederkirch" camps.
A certificate of death for Zadok van der Giessen as discovered there, stated that he died on 5 December 1942 in Camp Annaberg. In it was mentioned an official cause of death as “pulmonary tuberculosis and gangrene” (lungentuberkulose und gangraen).
The archives of the Jewish Council of Amsterdam list Zadok van der Giessen being deported from Camp Westerbork "eastward" on 2 October 1942.
Private collection of Edward Haduch, Kedzierzyn-Kozle (Poland), the official death certificate of Zadok van der Giessen, issued by German authorities (Standesamt) of Annaberg and the Archive of the Jewish Council of Amsterdam.
However, by establishing the date of death of Zadok van der Giessen, the official date is maintained as stated after the war by the Dutch Department of Justice.