He remained at the camp with commandant Josef Kramer and assisted in handing it over to British troops.

In Auschwitz, when asked by Ella Lingens-Reiner how he reconciled his actions with his ethical obligations as a physician, Klein famously stated: "My Hippocratic oath tells me to cut a gangrenous appendix out of the human body.

"[2][3][4]Klein and 44 other camp staff were tried in the Belsen Trial by a British military court at Lüneburg.

During the trial Anita Lasker testified that Klein took part in selections for the gas chamber.

[5] Klein was sentenced to death and hanged at Hamelin prison by Albert Pierrepoint on 13 December 1945.