During the German occupation of Poland (World War II), the Polish population was subject to mass arrests, executions, expulsions, deportations to Nazi concentration camps and confiscation of property. The "Einsatzgruppe VI" carried out public executions of Poles in the town on October 2 and October 23, 1939 as part of the "Intelligenzaktion", killing 8 and 18 people respectively, including activists, merchants, landowners, the director of the local narrow gauge railway, the chairman of the local branch of the "Sokół" Polish Gymnastic Society, principals of schools from Kościan and the nearby village of Borowo and one student. In Kościan, the Germans operated a prison for Poles from both the town and the region, many of whom were later transported to the infamous Fort VII in Poznań. On November 7 and 9, 1939, 66 Polish craftsmen, merchants, farmers, local officials and workers, previously held in the local prison were massacred in the nearby forest. Further such massacres were carried out by the Germans in December 1939 and in January and February 1940. The local high school principal was among Polish teachers and principals murdered in the Dachau concentration camp. Over 50 Poles, including local activists, intelligentsia and the families of victims of executions, were expelled in 1939, while 2,139 Poles were expelled in 1940, and their houses were then handed over to German colonists as part of the "Lebensraum" policy. 534 patients of the local psychiatric hospital were gassed by the Germans in January 1940, and afterwards patients from psychiatric hospitals in Germany were transported to Kościan and also gassed.