On the direct orders of Adolf Hitler carried out by Reinhard Heydrich 's bureau of '' Referat Tannenberg '' along with Heinrich Himmler 's '' SS '' - RSHA ( Main Security Office ) , Poles from among intelligentsia and elites were rounded up , and executed without any due process by the '' SS-Einsatzgruppen '' in dozens of remote locations such as the forest massacres in Piaśnica and the cavernous Valley of Death . Starting right after the invasion in September 1939 , with a second wave in the spring of 1940 , these actions were an early measure of the German '' Generalplan Ost '' colonization
Valley of Death
Valley of Death (Bydgoszcz)
Intelligenzaktion Pommern