Jacob Katwijk was the youngest of the two children of Abraham Katwijk and Betje Bierman. He was born on 24 May 1922 in Amsterdam and was working as an apprentice diamond worker. He was unmarried.
Jacob had an elder sister, Sara, who got married in December 1940 to the non-jewish Hendrik Frans Sonnen…
In addition, a Jokos file (number 15912) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.