Frederik Alter owned a nice building in the Keizerstraat where he had a souvenir shop. The family lived above the shop. According to tradition he was betrayed by his neighbour across the way when he had taken off his jacket with the obligatory Jewish star before dinner.
Addition of a visitor of the website
In addition, a Jokos file (number 34623) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.The Jokos file reveals that a claim was lodged for compensation for valuables surrendered to the Lippmann-Rosenthal looting bank (L-claim, number 170/193).