The Devil Bat (1941)

⁣Dr. Carruthers (Bela Lugosi), bitter at being betrayed by his employers when they became rich as a result of his invention, attains revenge by electrically enlarging bats and sending them out to kill his employers' family members. Johnny Layton (Dave O'Brien), a reporter, finally figures out Carruthers is the killer and arranges for him to become a victim of the very menaces he created.