To speed up the mass murder of Jews, the Nazis experiment with the use of poisonous gas in the Auschwitz concentration camp. The Chelmno killing centre is the first facility where prisoners are gassed in December 1941.
Jews from the Lodz ghetto are transferred to a new train at the Kolo train station during deportation to the Chelmno killing centre. Poland, 1942. (U.S. Holocaust Memorial Museum, courtesy of Sidney Harcsztark)