 Complete the following phrase:  The semi-industrial incineration of corpses at the Treblinka extermination camp began as soon as the political danger associated with the earlier burials was realised. In 1943, the 22,000 Polish victims of the Soviet Katyn massacre were discovered near Smolensk and reported to Adolf Hitler. Their remains were well preserved underground, attesting to the Soviet mass murder. By April 1943, Nazi propaganda began to draw attention of the international community to that war crime. The 