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 Jacob Raphaël Groen as discovered there, stated that he died on 27 December 1942 in Camp Annaberg. In it was mentioned an official cause of death as “gangrene and pneumonia” (Gangraen und Lungenentzündung).
The archives of the Jewish Council of Amsterdam list Jacob Raphaël Groen arriving 3 October October 1942 in Camp Westerbork and that presumably he had been deported "eastward" on 5 October 1942.
Private collection of Edward Haduch, Kedzierzyn-Kozle (Poland), the official death certificate of Jacob Raphaël Groen, issued by German authorities (Standesamt) of Annaberg and the Archive of the Jewish Council of Amsterdam.
However, by establishing the date of death of Jacob Raphaël Groen, the official date is maintained as stated after the war by the Dutch Department of Justice.