By establishing the date of death of Isaak Hilversum the official date is maintained as stated after the war by the Dutch Department of Justice.
In a document, which was a protocol of an on-site inspection conducted by Polish judicial authorities in March 1946 at the former camp of Blechhammer and at the mass burials site in the forest near the camp, another date of death for Isaak Hilversum is mentioned namely the 11th of October 1943. According to this protocol there were several still legible wooden markings on some of the graves. The information from the markings were included in the protocol.
In 1958 all remains from the forest cemetery of Blechhammer were exhumed and buried in a common grave at the Community Cemetery in Opole Polwies.
Source: Panstwowe Muzeum, Auschwitz-Birkenau, protocol 6th of March 1946