Reportedly outraged by the euthanasia or Aktion T4 programme, he decided to join the Waffen SS: "to look into the matter of these ovens and chambers in order to learn what happened there."[1] Because of his technical education, Gerstein was placed in the Waffen-SS technical disinfection services where he rose quickly to become its head. It was in that capacity that he traveled to the extermination camps of Belzec and Treblinka offering the supply of hydrogen cyanide (Zyklon B).[2]