Belle Mayer trained as a lawyer and worked for the General Counsel of the US Treasury, Foreign Funds Control Bureau. This bureau worked to enforce the Trading With the Enemy Act passed by Congress. In this capacity, Mayer became familiar with the German I. G. Farben chemical company, a large conglomerate that used slave labor during World War II. In 1945, Mayer was sent as a Department of Treasury representative to the postwar London Conference. She was present as representatives from the Allied nations outlined the principles of law for the prosecution and trial of Europe's major war criminals. Mayer reported to this commission as it prepared for upcoming war crimes trials. She was then among the attorneys (including her future husband William Zeck) who prepared the indictment against the I. G. Farben company at the Nuremberg trials.
I think it was a very very rough experience, I think I was not prepared for it, probably, emotionally. Not mature enough to handle this constant assault on the senses and my husband has told me several times that it was a great, one of the greatest chapters in the lives of everybody who was at Nuremberg and years ago, not recently, not in many years, but years ago I used to say that it was an experience that one did not have to have, because it was pretty shattering emotionally. However, he may be right and I may be wrong. It certainly has had an impact on my life.