After the failure of Stauffenberg's attempt to kill Hitler, Maaß was arrested on 8 August 1944, and imprisoned at Ravensbrück concentration camp. He was charged at the Volksgerichtshof for his involvement in the resistance movement next to Adolf Reichwein, Julius Leber and Gustav Dahrendorf. Maaß, Reichwein and Leber were sentenced to death on 20 October 1944, with Maaß and Reichwein executed the same day at 3.40 p.m. at Plötzensee prison.