On 14 June 1946, Professor Julius Hallervorden, director of the Section for Histopathology at the Kaiser Wilhelm Institute for Brain Research (KWI für Hirnforschung, KWIHF), experienced the surprise of his life. Completely unexpectedly, the neurologist and psychiatrist Professor Leo Alexander, a Jew who had been forced to leave Germany in 1933 and was now conducting numerous interviews with German neurologists, psychiatrists, and neuropathologists on behalf of the American military government, appeared in Dillenburg, Hessia, where Hallervorden had landed with his department in 1944. Believing Alexander to be an ally in the struggle to preserve the KWIHF, Hallervorden threw caution to the wind and acknowledged forthrightly that in his department he had studied hundreds of brains that came from mentally ill and mentally disabled patients who had been killed in the course of the Nazi “euthanasia” program.

As far as his visitor's intentions were concerned, Hallervorden could not have been more wrong. Alexander's mission was to investigate the state of research achieved in National Socialist Germany; at the same time, he was collecting material to prepare charges in the Nuremberg Physicians' Trial. While no preliminary proceedings against Hallervorden were opened and he was not charged, his remarks in conversation with Alexander resulted in his role in “euthanasia” becoming public, so that in the aftermath – for instance, in connection with the Fifth International Congress of Neurology in Lisbon in 1953 – intense controversies about Hallervorden's wartime activities erupted on numerous occasions.