A few postcards and a letter remain that Isaac Hollander (known as Ies) sent his parents from Mauthausen and Buchenwald.
Jewish Historical Museum, Documents collection, inv.nr 6100 t/m 6102
De briefkaart die Isaac Hollander vanuit Buchenwald stuurde is hier te lezen: http://bit.ly/1U6zUtz .
De briefkaart uit Mauthausen is hier te zien: http://bit.ly/1JmtM8A .
In addition, a Jokos file (number 31801) on this household is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.