Hartheim castle, a euthanasia killing center where people with physical and mental disabilities were killed by gassing and lethal injection. Hartheim, Austria, date uncertain. Photograph »

Buses that transported patients from a public hospital near Wiesbaden to the Hadamar euthanasia center, where the patients were gassed or killed by lethal injection. Germany, between May and September 1941. Photograph »

In August 1943 a gas chamber was installed in this building, seen here after the liberation of the camp, in the Natzweiler-Struthof concentration camp. France, 1945. Photograph »

Interior of a gas chamber at the Majdanek camp. Majdanek, Poland, after July 24, 1944. Photograph »

Zyklon B pellets found at the liberation of the Majdanek camp. Poland, after July 1944. Photograph »

Gas chamber in the main camp of Auschwitz immediately after liberation. Poland, January 1945. Photograph »