According to the "Sterbebücher" (death records) of Auschwitz, Isaac Ritmeester was murdered there on 8 August 1942. This date however differs one day with the official date of death of 9 August 1942, as determined by the Dutch Ministry of Justice after the war. For the time being however, the website joodsmonument.nl, list only the dates of death, as published at the time in the "Nederlandse Staatscourant" (Dutch Government Gazette) by the Ministry of Justice.
Death of Isaac Ritmeester according the Auschwitz Sterbebücher (death index).
The official death certificate of Isaac Ritmeester no.420 of 8 September 1950.