In 1942, mass transports of European Jews started to come to KL Auschwitz II – Birkenau, which was the way of implementing the plan of total extermination of the Jewish population. Then, the Germans started to erect a complex of four huge crematoria, which were completed between March and June of 1943 – that terrifying and most tragic machine of the Holocaust. Before his escape, Witold Pilecki had seen the beginnings of the murderous practices and wrote about them in his reports, also in the report of 1943. The information reached the Allied countries via the Polish Government in London.