Polish historians, such as Madajczyk, Jastrzębski, Karol Marian Pospieszalski, Ryszard Wojan, and others claim that the killings were triggered when the ethnic Germans, dressed as civilians, opened fire on the Polish troops (Jastrzebski later changed his views after starting to work with German expelee organizations). The Poles retaliated, killing many and executing prisoners afterwards. Polish historians like Pospieszalski and Janusz Kutta point to a Nazi top secret false flag Operation Himmler (which took place on August 31 – September 1) and was designed to create an illusion of Polish aggression against Germany. Thus it is argued that actions like the Gleiwitz incident and events in Bydgoszcz were all part of a larger Nazi plan to discredit the Poles. Polish historians such as Pospieszalski and Wojan argue that the German fifth column agents (or their higher-ups) might have been deliberately aiming to produce a situation likely to result in German civilian casualties as a way to fuel Nazi propaganda. This argument has been criticized: Harry Gordon questions whether the Germans were willing to sacrifice their citizens for propaganda gains.