 Klug's name appeared in an advertisement in several Hamburg which listed a number of teachers "on leave from the schools service" ("""aus dem Schuldienst beurlaubt""").Klug had already had his apartment searched by police in May 1933, and been arrested while at school, but he had on that occasion been released for lack of evidence.Towards the end of the summer he was arrested again, and on 4 October 1933 condemned to a year in prison for "preparing high treason" (""Vorbereitung zum Hochverrat"").