At Auschwitz, the actual delivery of gas to the victims was always handled by the SS, on the order of the supervising SS doctor.[316][317] Many of the SS doctors also conducted inhumane medical experiments on camp prisoners.[318] The most infamous SS doctor, Josef Mengele, served as a medical officer at Auschwitz under the command of Eduard Wirths of the camp's medical corps.[319] Mengele undertook selections even when he was not assigned to do so in the hope of finding subjects for his experiments.[320] He was particularly interested in locating sets of twins.[321] In contrast to most of the doctors, who viewed undertaking selections as one of their most stressful and horrible duties, Mengele undertook the task with a flamboyant air, often smiling or whistling a tune.[322][323] After the war, many SS doctors were charged with war crimes for their inhumane medical experiments and for their role in gas chamber selections.[324]