Polish resistance members, policemen, teachers and school and university students. An attempt to "Germanise" the city led to an influx of the ethnic Volksdeutsche, increasing the number of German minority from 10 to 15% in 1939 to 20–25%. Near Lublin, the so-called 'reservation' for the Jews was built based on the idea of racial segregation known as the "Nisko or Lublin Plan". The Germans established and operated a Baudienst forced labour camp for Poles in Lublin. Many Poles from or associated with Lublin, including 94 lecturers, alumni and students of the Catholic University of Lublin were murdered by the Soviets in the large Katyn massacre in April–May 1940. The Jewish population was forced into the newly established Lublin Ghetto near Podzamcze. The city served as headquarters for Operation Reinhardt, the main German effort to exterminate all Jews in occupied Poland. The majority of the ghetto inmates, about 26,000 people, were deported to the Bełżec extermination camp between 17 March and 11 April 1942. The remainder were moved to facilities around the Majdanek concentration camp established at the outskirts of the city. Almost all of Lublin's Jews were murdered during the Holocaust in Poland. The secret Polish Council to Aid Jews "Żegota", established by the Polish resistance movement operated in the city. There are also known cases of local Polish men and women, who were captured and sent to either forced labour or concentration camps by the Germans for sheltering and aiding Jews. Poles who saved Jews in other places in the region were also temporarily imprisoned in the local castle, before being sent to the Auschwitz concentration camp. After the war, some survivors emerged from hiding with the Christian rescuers or returned from the Soviet Union, and re-established a small Jewish community in the city, but their numbers were insignificant. Most survivors left Poland for Israel, the United States and other countries. In the first years of the occupation, many expelled Poles from Gdańsk and German-annexed Pomerania were deported to Lublin, and later on, in 1943, around 9,000 expelled Poles from the nearby Zamojszczyzna region were brought to Lublin and imprisoned in the Majdanek concentration camp and in a transit camp at Krochmalna Street; many were afterwards deported to forced labour in Germany. In August 1943, thanks to efforts of the Polish Rada Główna Opiekuńcza charity organisation, around 2,200 people were released from those two camps. Many of the released