During the war, Hartog IJzerman's brother Lucas, and his wife Clara lived with the IJzerman family for some months. Eventually, both IJzerman families were deported together, first to Westerbork and later to Sobibor.
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In addition, a Jokos file (number 31060) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.