Hirsch met repeatedly with Strasser and Grunov, a leader in the Black Front. They both worked on Hirsch's idealism and desire to devote himself to a cause. They urged Hirsch to action, arguing that he must act to show that Jews were not afraid to stand up for themselves, and his "heroic act" would inspire Jews throughout Germany. Seduced by their arguments, Hirsch agreed to be part of an anti-Nazi plot.
The plan was for Hirsch to take a bomb in a suitcase and blow up the Nazi Party headquarters in Nürnberg. What Hirsch didn't realize was that the bomb was constructed to kill him along with destroying the Nürnberg building. Furthermore, the Nazis were informed of Hirsch's entry into Germany. Whether this was by a Gestapo infiltrator or by Grunov himself remains unclear to this day. There are indications that the Black Front thought Hirsch's capture and trial by the Nazis would bring better publicity to the Black Front movement than the bombing of the Nürnberg Nazi headquarters. But however it came about, Helmut Hirsch was arrested in December 1936 for treason against the German Republic, before he could carry out his attempt to bomb the Nürnberg building.
Hirsch went on trial in March of 1937, in front of a secret session of the infamous People's Court. Hirsch was calm and unwavering, and he admitted his guilt. His family desperately tried to get the United States government involved, based on the disputed fact the Hirsch was an American citizen. William Dodd, the American ambassador to Germany, made a valiant effort to get Hitler to pardon Hirsch. It was all to no avail. On June 4, 1937 Helmut Hirsch was executed by the Nazi government.