 Complete the following phrase:  On September 1, 1939, the first day of the German invasion of Poland and World War II, there was a skirmish between German saboteurs and the Polish self-defense in the present-day district of Michałkowice. German saboteurs then entered the local mine, taking several dozen Polish miners as hostages. After a battle, Polish troops and volunteers, including members of the Sokół Polish Gymnastic Society and boy scouts, recaptured the mine. There were deaths on both sides, and the Poles also captured dozens of German saboteurs. The Germans eventually invaded and captured the city in the following days, and already on September 8, 1939, the German Freikorps murdered six Poles in the city. In September 1939, the German Einsatzgruppe I operated in the city and committed various 