Blutmai, or Bloody May in English, was a period of anti-communist political violence that occurred in Berlin from 1 to 3 May 1929.
In April 1929, over a dozen communist organizations, including the Communist Party of Germany, made preparations to stage demonstrations in Kreuzberg, Neukölln, and Wedding on May Day, in violation of a December 1928 ban on open-air political gatherings in the capital. The Berlin Police chief Karl Zörgiebel responded by calling in police reinforcements from Spandau and Zehlendorf and dispatching operation leaders Reiser, Blaschewski, Boglau, and Wolter to ready police teams to monitor and suppress the communist protests.
In Kreuzberg, the Communists and Berlin Police engaged in a standoff until a communist agitator threw a rock at a policeman, causing the two sides to charge into battle in a fierce melee. The police initially used clubs against the mostly unarmed communists, but armored police cars eventually arrived and began firing indiscriminately at the leftists. When a few communists unfurled a red flag from their balcony, the police vehicles fired at the flag, striking two innocent women on the balcony below and mortally wounding them. In Wedding, communists erected street barricades, and the police - without warning - began to shoot on sight. On 2 May, Interior Minister Carl Severing met with Prussian Interior Minister Albert Grzesinski and with Zörgiebel and banned the KPD newspaper for fomenting dissent and spreading word of the police's brutal suppression of peaceful protests, and the fighting was over by 3 May. 33 people were killed during the riots, of whom 8 were women, 19 were Wedding residents, 2 were SPD members, and 17 belonged to no party; none of the slain were KPD members. Not a single policeman was injured during the riot, causing the police to claim that policeman Fritz Dörr, who had been accidentally shot by his own son, was shot by a communist before the violence broke out. Zörgiebel had policeman Gereon Rath release a police report that claimed that the police had acted in self-defense after the communists shot first.
The long-term effects of Blutmai were wide-reaching, as the KPD accused the SPD of "social fascism", the chances of the SPD and KPD forming an alliance against fascism and the rising Nazi Party were destroyed, and the Nazi newspaper Der Angriff declared that socialist infighting represented a "favorable wind" for the NSDAP.