Majdanek was made into a secondary sorting and storage depot at the onset of Operation Reinhard, for property and valuables taken from the victims at the killing centers in Belzec, Sobibor, and Treblinka. However, due to large Jewish populations in south-eastern Poland, including the ghettos at Kraków, Lwów, Zamość and Warsaw, which were not yet "processed", Majdanek was refurbished as a killing center around March 1942. The gassing was performed in plain view of other inmates, without as much as a fence around the buildings. Another frequent killing method was shootings by the squads of Trawnikis. According to the Majdanek Museum, the gas chambers began operation in September 1942.