The Holocaust
Himmler changed efficient methods of killing
Poland
Himmler and his subordinates in the field feared that the murders were causing psychological problems for the SS, and began searching for more efficient methods. In December 1941, similar vans, using exhaust fumes rather than bottled gas, were introduced into the camp at Chełmno, Victims were asphyxiated while being driven to prepared burial pits in the nearby forests.