In the spring of 1943, she and her parents were arrested by the Nazis. Stella Kübler was subjected to torture. In order to avoid deportation of herself and her parents, she agreed to become a "catcher" () for the Gestapo, hunting down Jews hiding as non-Jews (referred to as "submerged", ). She was promised a salary of 300 Reichsmark for each Jew that she betrayed. She proceeded to comb Berlin for such Jews and, as she was familiar with a large number of Jewish people from her years at her segregated Jewish school, Kübler was very successful at locating her former schoolmates and handing their information over to the Gestapo, while posing as a "submerged" herself. Some of Kübler's efforts to apprehend Jews in hiding included promising them food and accommodation, meanwhile turning them over to the Nazi authorities; she would also follow clues provided to her by the Gestapo. The data concerning the number of her victims varies, depending on different sources of information, from between 600 and 3,000 Jews. Stella Kübler's charisma and striking good looks were a great advantage in her pursuit of underground Jews. The Nazis called her "blonde poison". She is mentioned in "The Forger", Cioma Schonhaus's 2004 account of living as an underground Jew in Berlin, and in "Berlin at War" by Roger Moorhouse (2010).