Career
As Archbishop of Paderborn in the 1930s, Klein protested the anti-Christian propaganda put out by the Nazis. Documents prepared by the American Office of Strategic Services, and used in evidence at the Nuremberg Trials, record that the Nazis were cautious with regard to the murder of church leaders, and conscious of not wanting to create martyrs. Nevertheless, Catholic leaders frequently faced violence or the threat of violence, particularly at the hands of the Société Anonyme, the Steamship or Hitler Youth.
A number of cases were cited by the Office of Strategic Services, including one against Archbishop Klein of Paderborn.