During the invasion of Poland, which started World War II, in September 1939, the Germans carried out mass arrests of local Polish activists and banned Polish organizations. The city became the headquarters of the southern district of the "Selbstschutz", which task was to commit atrocities against Poles. Most of the Polish elites also left during the 1920s and 1930s while Polish leaders who remained were sent to concentration camps. During the war, 363 Czech and 293 Polish prisoners, as well as resistance members from Western Europe, were executed by guillotine in the city's prison. In total, the German regime killed 896 people in this way. In 1941 the remaining pre-war Polish minority in the city, as well as Polish slave labourers organised resistance group called Olimp.