From 1940 onward the Home Army courier Jan Karski delivered the first eyewitness account of the Holocaust to the Western powers, after having personally visited the Warsaw Ghetto and a Nazi concentration camp. Another crucial role was played by Witold Pilecki, who was the only person to volunteer to be imprisoned at Auschwitz (where he would spend three and a half years) to organize a resistance on the inside and to gather information on the atrocities occurring there to inform the Western Allies about the fate of the Jewish population. Home Army reports from March 1943 described crimes committed by the Germans against the Jewish populace. Rowecki estimated that 640,000 people had perished in Auschwitz between 1940 and March 1943, including 66,000 ethnic Poles and 540,000 Jews from various countries (this figure was revised later to 500,000). The Home Army started carrying out death sentences for szmalcowniks in Warsaw in the summer of 1943.