On September 3 and 4, 1939, in Bydgoszcz, Poland, German military intelligence units caused a panic that resulted in the littering of Bydgoszcz and surrounding areas with the bodies of German victims of the Polish military insurrection.

 　　On September 3 and 4, 1939, a genocide massacre took place in Bydgoszcz, Poland. From the panic created by German military intelligence (PK 689), the bodies of German victims of the Polish military insurrection in Bydgoszcz and the surrounding area were scattered. Retreating Polish troops of the 15th Infantry Division of the Pomeranian Army were fired upon by unidentified perpetrators, and there were also attacks against Polish civilians. About 20 Polish soldiers and five Bydgoszcz residents were probably killed, leading to a violent backlash by Polish military authorities. As a result of the rioting that took place in the city, between 160 and more than 400 people were captured and shot, depending on the source.

　The Germans began their retaliatory actions shortly after September 5, when they occupied Bydgoszcz Street. Between 350 and 400 people were shot dead in public executions. The most spectacular crimes took place in Bydgoszcz Market Square on September 9 and 10. In the following months, about 1,500 people were killed in the so-called Valley of Death in Fordon, near Bydgoszcz.

　The Germans used the events in Bydgoszcz for propaganda purposes: September 3 was marked as Blood Sunday (Bromberger Blutsonntag) and was first published in a German newspaper (Deutsche Rundschau) published in Bydgoszcz on September 7, 1939. The incident became the pretext for bloody revenge against Poles throughout Pomerania. Nazi propaganda exaggerated that the Poles had killed 1,000 people in Bydgoszcz alone. The Germans claimed that it was an organized military action by Polish forces in Pomerania.

　Britain and France declared war on Germany on September 3, 1939, at which point Germany forced an attack and the Polish army held out for seven days before finally surrendering. It then triggered the nearly six-year-long World War II that tore Europe apart and resulted in the deaths of some 70 million people.

　After World War II, from 1945 to 1948, the Commission of Inquiry into German Crimes in Poland conducted an investigation. It found that "the Germans carried out a planned diversionary operation at 10:15 a.m. on September 3, 1939, to create panic among retreating Polish regiments in Bydgoszcz." Based on eyewitness testimony, the Prosecutor's Office established that there were 46 points in Bydgoszcz where saboteurs fired. A Polish investigation concluded in 2004 that approximately 40 to 50 Poles and 100 to 300 Germans were killed. It was one of many false flag operations launched by the Germans under the code name Operation Himmler.