His operations were so successful that the Germans instituted a special manhunt to get him and his team and on 13 January 1944 the Gestapo arrested him and agent Yolande Beekman in the Café Moulin Brulé in Saint-Quentin. At the Gestapo headquarters there the two were tortured repeatedly but never broke and a few months later Biéler was transferred to Flossenbürg concentration camp in the Oberpfalz region of Bavaria, where the brutal torture continued. According to his daughter Jacqueline Bieler's research, prisoners at Flossenburg were called "Nacht und Nebel", (Night and Fog). "When you were designated an NN prisoner, you were meant to disappear. If the Red Cross asked questions about you, they weren't supposed to find out anything."