by advance units of the German regular army (Heer), or that the shots were fired by Polish soldiers in the confusion of the mass withdrawal. Von Frentz claims that Polish troops and civilians massacred German civilians due to confusion. Polish historians feel the German historiography is based on Nazi German sources, ignoring numerous Polish sources. 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. Recent discussion The modern consensus among Polish historians is that the events constituted an attack on the Polish population and military by German militia. In 2004, historian Tomasz Chinciński in a publication of Institute of National Remembrance (IPN) summarized recent research related to Bloody Sunday, confirming that the majority of historians agree that an "insurrection" by agents who had arrived from the Third Reich as well as some German inhabitants of Bydgoszcz took place. He has published a work detailing new evidence of German diversionary activity in September 1939 in Poland. There are numerous Polish eyewitness accounts of action of a German fifth column which included members of local minority; Pospieszalski cited multiple witnesses for at least 46 cases of German civilians opening fire on Polish troops. There are numerous Polish Army reports and German documents confirming the saboteur actions of armed German Poles in other cities. According to German historians, any members of the fifth column, if present in the city, were infiltrators from Germany, not