In the immediate aftermath of the Reichstag fire the authorities concentrated their harassment/persecution on political activists identified as communists. Many were arrested and others fled abroad. On 30 August 1930, however, after he returned from one of his trips, Otto Brenner was arrested and taken into investigatory custody. During the eighteen months of uncertainty that followed he was permitted to remain in touch with his wife by letter. The charge, when it came on 9 May 1935, was the usual one under these circumstances: "Preparing to commit high treason" ("Vorbereitung zum Hochverrat"). The verdict was largely a foregone conclusion, but the sentence, delivered by the on 25 June 1935, was relatively mild. He was sentenced to a two-year jail term. This had largely been spent in pre-trial detention, and a few months later he was able to return to his wife in . He remained under police surveillance till the end of the 1939-45 war, however.