English: The Liberation of Bergen-belsen Concentration Camp, April 1945 Dr Fritz Klein, the camp doctor, standing in a mass grave at Belsen. Klein, who was born in Austro-Hungary, was an early member of the Nazi Party and joined the SS in 1943. He worked in Auschwitz-Birkenau for a year from December 1943 where he assisted in the selection of prisoners to be sent to the gas chambers. After a brief period at Neungamme, Klein moved to Belsen in January 1945. Klein was subsequently convicted of two counts of war crimes and executed in December 1945.