Jacob Koker and Sara Gobetz married in 1924 in Amsterdam. They moved in 1943 from Hilversum to Amsterdam.
Stadsarchief Amsterdam, archiefkaart Jacob Koker
In addition, a Jokos file (number 32449) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.