The Germans became aware of the political danger associated with the mass burial of corpses in April 1943 , when they discovered the graves of Polish victims of the 1940 Katyn massacre carried out by the Soviets near Smolensk . The bodies of the 10,000 Polish officers executed by the NKVD were well preserved despite their long burial . The Germans formed the Katyn Commission to prove that the Soviets were solely responsible , and used radio broadcast and newsfilm to alert the Allies to this war crime . Subsequently , the Nazi leadership , concerned about covering up their own crimes , issued the secret orders to exhume the corpses buried at death camps and burn them instead . The cremations began shortly after Himmler 's visit to the camp in late February or early March 1943
Katyn massacre
Katyn massacre
Treblinka extermination camp