Vernichtungslager Treblinka
After the war, Ząbecki testified at the trials of German war criminals, including "SS" officer Kurt Franz, and the commandant of Treblinka extermination camp, Franz Stangl. His incriminating evidence against them included original German waybills , which proved that the "Güterwagen" boxcars crammed with prisoners on the way to Treblinka extermination camp, were returning empty. Ząbecki secretly stole a batch of waybills in 1944 from the control house to serve as physical proof of the massacre. From July 1942 until the end of war, Ząbecki regularly delivered his reports about the Holocaust trains to the Polish government-in-exile.