In 1941 Halem broke contact with Römer who agreed to continue with the plan but still hesitated to act. In early 1942, Römer was arrested by the Nazi police and under torture revealed the assassination plot. Halem was arrested on 26 February 1942 by the Gestapo and suffered torture through a number of prisons and concentration camps, including Sachsenhausen, but did not reveal any of his fellow conspirators. In June 1944, shortly before the 20 July 1944 coup attempt, the People's Court indicted Halem for conspiracy to commit treason and undermining the war effort. He was sentenced to death and executed by guillotine in Brandenburg-Görden Prison on 9 October 1944.