Hilberg was undecided under whom he should carry out his doctoral research. Having attended a course on international law, he was also attracted to the lectures of Salo Baron, the leading authority on Jewish historiography at the time, with particular expertise in the field of laws pertaining to the Jewish people. According to Hilberg, to attend Baron's lectures was to enjoy the rare opportunity of observing "a walking library, a monument of incredible erudition", active before his classroom of students. Baron asked Hilberg whether he was interested in working under him on the annihilation of Europe's Jewish population. Hilberg demurred on the grounds that his interest lay in the "perpetrators", and thus he would not begin with the Jews who were their victims, but rather with what was done to them.