Standing in the path of the German army's advance during the early days of the invasion, tensions quickly escalated in Bydgoszcz between the city's sizable German-speaking minority and its Polish majority.
[4] The term "Bloody Sunday" was applied to the events by Nazi propaganda officials, who highlighted and exaggerated German casualties.
[7] Additionally, fifty Polish prisoners of war from Bydgoszcz were accused by Nazi summary courts of taking part in "Bloody Sunday" and shot.
The reprisals compounded violence stemming from the German attempts to pacify the city, and the premeditated murder of notable Poles as part of Operation Tannenberg.
Adolf Hitler revitalized the Völkisch movement, making an appeal to the German minority living outside of Germany's post-World War I borders and recruiting its members for Nazi intelligence.
By March 1939, these ambitions, charges of atrocities on both sides of the German-Polish border, distrust, and rising nationalist sentiment in Nazi Germany led to the complete deterioration of Polish-German relations.
After armed conflict erupted on 1 September 1939, ethnic Germans living in Poland were in many places subjected to attacks, and the Polish government arrested ten to fifteen thousand on suspicion of being loyal to Germany, marching them toward the east of the country.
[1][3] As the Wehrmacht's Fourth Army prepared to storm the city of Bydgoszcz on 3 September, the violence intensified, resulting in the deaths of up to 300 ethnic Germans and 40 to 50 Poles.
[3] Beginning in early September, the Abwehr reported in documents prepared by general Erwin von Lahousen that German armed saboteurs conducting operations behind the front line in Bydgoszcz suffered heavy losses.
In addition to this group a 10-member combat unit under command of a German named Otto Meister was also formed in Bydgoszcz and received orders from Wroclaw local office of Abwehr.
[16] By the end of August just before the invasion took place Polish police conducted several arrests during which they found explosives, armbands and guns.
[19] In the ensuing fight both sides suffered some casualties; captured German nonuniformed armed insurgents were executed on the spot and some mob lynching was also reported.
[4] The German forces which entered the city also encountered resistance from members of the paramilitary Citizen Watch (Straż Obywatelska), particularly in the Szwederowo neighborhood, which was predominantly inhabited by working-class individuals.
[22] The Citizen Watch in Bydgoszcz relinquished its weapons after receiving assurances from General Eccard von Gablenz, commander of the Kampgruppe "Netze", that its members would be treated in accordance with international law as POWs.
The most reliable estimates put the total number of ethnic Germans killed in outrages, forced marches, bombing and shelling at around 4,000.
They did not remotely compare with, let alone provide any justification for, the calculated savagery of the treatment meted out by the German masters, directed at wiping out anything other than a slave existence for the Polish people.
[28][20] In an act of retaliation for Bloody Sunday, a number of Polish civilians were executed by German military units of the Einsatzgruppen, Waffen SS, and Wehrmacht.
[28][29] The assurances issued to the Citizen Watch which surrendered after being promised that they were to be treated in accordance with international law as POWs were not upheld by the Germans.
[23] The remaining POWs, which included the leaders of the Citizen Watch, Konrad Fiedler and Marian Maczuga, were executed by gunfire in the Bielawki neighborhood of Bydgoszcz.
[30][31] Additionally, in the Boryszew massacre fifty Polish prisoners of war from Bydgoszcz were accused by Nazi summary courts for taking part in "Bloody Sunday" and shot.
[34] The German governor, General Walter Braemer, (the commander of the rear army area), ordered the execution of 80 Polish hostages over the next few days.
These victims included the mayor of Bydgoszcz, Leon Barciszewski [pl] Many of those killings took place in a part of the city that became known as the Valley of Death.
[46] This debate has been resolved by investigation of German archives, which confirmed existence of several diversion and saboteur groups in Bydgoszcz overseen by intelligence organizations by Nazi Germany.
[60] Chinciński discussed newly discovered documents of the Abwehr that show that there were indeed plans for fifth column and diversion activities in Bydgoszcz; several paramilitary groups were organized by Germany in the city, he discussed the bias of the Polish communist era historiography, which minimized cases of Polish mob lynching of ethnic Germans, which did occur in Bydgoszcz.