The American Alsos Mission, a scientific intelligence-gathering task force, followed behind the advancing Allied armies in the west, looking for evidence of a German atomic bomb. Its scientific leader, the physicist Samuel Goudmit, quickly determined that the Germans were far removed from building nuclear weapons but also was misled by some documents and his own prejudices, convincing himself that the Germans, including his colleague Werner Heisenberg, had not understood how an atomic bomb would work. When Goudsmit returned to the United States, he began publishing books and articles using the German uranium work as an example of how the Nazis had ruined science through political and ideological control, mistakes that America must not repeat. Heisenberg responded by defending both his scientific work and conduct under Hitler. Goudsmit criticized both Heisenberg and Carl Friedrich von Weizsäcker for compromising with the Nazis. While Goudsmit eventually reconciled with Heisenberg, he never forgave Weizsäcker. Goudsmit had lost his parents in Auschwitz, and Weizsäcker’s father, a high-ranking official in the Foreign Ministry, had been convicted of war crimes.