Abbott and Costello Meet the Killer, Boris Karloff (1949)

Lost Caverns Hotel bellhop Freddie Phillips is suspected of murder. Swami Talpur tries to hypnotize Freddie into confessing, but Freddie is too stupid for the plot to work. Inspector Wellman uses Freddie to get the killer (and it isn’t the Swami).
Charles Barton
Bud Abbott, Lou Costello, Boris Karloff, Lenore Aubert, Gar Moore, Donna Martell, Alan Mowbray, James Flavin, Roland Winters, Nicholas Joy, Mikel Conrad, Morgan Farley, Victoria Horne, Percy Helton, Claire Du Brey, Harry Hayden, Vincent Renno, Gail Bonney, Marjorie Bennett, Harry Brown, William H. O’Brien, Arthur Hecht, Billy Gray, Murray Alper, Bobby Barber
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