In 1934, on his release from the concentration camp, Weidauer undertook further work for the Communist Party, which now counted as illegal activity. During 1934 and 1935 he underwent further terms of "investigatory detention" in Schwarzenberg and Dresden. At the end of September 1935 he emigrated to Prague. In December 1936 he moved on to Denmark where, using the cover name "Karl Förster", he worked with the northern regional German Communist Party (now in exile). In April 1938, "in absentia", he had his German citizenship withdrawn. In April 1940 Denmark was occupied by the German army and Weidauer was interned. At the start of 1941 he was returned to Germany by the police and after a further period of detention on 3 June 1942 he was put on trial (briefly) in the People's Court ("Volksgerichtshof"), a special court set up by the government outside the constitutional frame of law and used for trials involving a widely drawn range of "political offenses". He received the conventional fifteen-year prison sentence for "Preparing to commit High Treason". For over three years he was held in a succession of prisons including those at Brandenburg-Görden, and Leipzig. In February 1945, after the Destruction of Dresden, Weidauer was part of a Prisoners' Detachment moved to the city to help make a start on clearing the residual rubble. His detention was ended on 7/8 May 1945 when the Red Army arrived in Dresden.