On the morning of 21 October, the assembled men and boys were marched to a field outside the town. Over a period of seven hours, they were lined up in groups of 50 to 120 and shot with heavy machine guns. "Go ahead and shoot", said an elderly teacher, "I am conducting my class". He was shot together with his students. As they faced the firing squad, many hostages sang the patriotic song "Hey, Slavs", which became Yugoslavia's national anthem after the war. One German soldier was shot for refusing to participate in the killings. A German report stated: "The executions in Kragujevac occurred although there had been no attacks on members of the Wehrmacht in this city, for the reason that not enough hostages could be found elsewhere." Even some German informants were inadvertently killed. "Clearly", the Holocaust historian Mark Levene writes, "Germans in uniform were not "that" particular about who they shot in reprisal, especially in the Balkans, where the populace were deemed subhuman."