Kosman van der Poorten lived in the Spoorstraat 22 in Zandvoort. On a list of Jewish companies sent by Zandvoort town to the Wirtschaftsprüfstelle on 26 July 1941, he was listed as the owner of a chemist shop.
A.E. Speijer, Zandvoorts wijzen kwamen uit het oosten (Zoetermeer 1995) 83
In addition, a Jokos file (number 15133) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.