He joined board of the Friedrich Krupp AG in 1934 as Director of Administration and Finance. From 1939 he was also on the board of Dresdner Bank. In 1943 Karl Goerdeler convinced him of the necessity of a coup to overthrow Hitler. If the July 20 Plot assassination attempt had succeeded he was earmarked to be the Minister of Finance. He was arrested in its aftermath and on 20 October 1944 was tried by the People's Court, but he succeeded in convincing Roland Freisler that he was suffering from memory loss. Avoiding conviction he was committed to a sanatorium and survived the war.
In 1947 he was indicted at the Krupp Trial for war crimes, including use of slave labor and plunder of occupied Europe. Following his conviction in 1948 he was imprisoned for seven years. He died in 1970 aged 82.