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 Sonnenschein and has survived the war. At the other hand, Jacob has been caught during the raid of 11 June 1941 and eventually ended up in Mauthausen via camp Schoorl. He lost his life in Mauthausen on 16 September 1941.
Sources include the City Archive of Amsterdam, archive cards of Abraham Katwijk and Jacob Katwijk, the Wikipedia website Razzia van Amsterdam (dutch language only) and the certificate of death for Jacob Katwijk nr. 289 dated 23 May 1950 from the A-register 34-folio 50verso, made out in Amsterdam.