In the autumn of 1942, Jewish leaders who smuggled Karski into the Ghetto arranged for him to visit a German Nazi transit camp to witness Jews being herded onto trains, to be sent to their deaths. Karski entered the Izbica transit camp in disguise. For years he thought he had been in the concentration camp in Bełżec, as he described it in his 1944 book, "Story of a Secret State." Later he recalled this dreadful experience in his interview for Claude Lanzmann’s "Shoah."