 Bela Lugosi (qv) was originally cast as Dr. Sovac and  Boris Karloff (qv) as Kingsley/Cannon, but Karloffs  interpretation of the gangster was unconvincing and he was replaced  by Stanley Ridges (qv). Karloff instead got the role as Dr. Sovac  and Lugosi got a minor role, although his second billing remained.  (Bojarski, "The Films of Bela Lugosi", 1980)