To control the population, prominent citizens and intellectuals, particularly Jews and Poles, were either confined in ghettos or transported to execution sites such as the Gestapo prison on Pełczyńska Street, the Brygidki Prison, the former military prison at Zamarstynów and to the fields surrounding the city — in the suburb of Winniki, the Kortumówka hills and the Jewish Cemetery. Many of those killed were prominent leaders of Polish society: politicians, artists, aristocrats, sportsmen, scientists, priests, rabbis and other members of the intelligentsia. This mass murder is regarded as a pre-emptive measure to keep the Polish resistance scattered and to prevent Poles from revolting against Nazi rule. It was a direct continuation of the infamous "Ausserordentliche Befriedungsaktion", one of the early stages of "Generalplan Ost", after the German campaign against the USSR started and the eastern half of prewar Poland fell under German occupation in place of that of the Soviet Union. One of the earliest Nazi crimes in Lwów was the mass murder of Polish professors together with some of their relatives and guests, carried out at the beginning of July 1941.