Someone denounced Katzenberger to the authorities and he was arrested on 18 March 1941 under the so-called Rassenschutzgesetz, or Racial Protection Law, one of the Nuremberg Laws, which made it a criminal offence as Rassenschande ("racial defilement") which prohibited Aryans and non-Aryans from having sexual relations.
As he desisted, he was arrested on suspicion of Rassenschande and taken to the regional court II, where he remained imprisoned for six weeks.