The Vampire Bat 1933

"The city of Kleinschloss is infected with a dark scourge from the past. A Legion of bloodsucking creatures who can assume human form have returned to prey upon the unsuspecting citizens. Detective Karl Brettschneider begins investigating numerous gory deaths at the request of the burgomaster. Despite the obvious evidence, he refuses to accept the existence of vampiric human bats, but soon their existence proves all too real."~YouTube link