"Behind the Mask" (1932) A Columbia Photoplay

A federal agent (Holt) goes undercover to infiltrate a drug smuggling operation headed by a mysterious Mr. X (Van Sloan), a criminal mastermind whose identity is unknown even to his henchmen. Mr. X is also running a bogus hospital where victims are killed on the operating table, and their coffins stuffed with narcotics. The drug-filled coffins are then buried in a cemetery.
Jack Holt as Jack Hart aka Quinn
Constance Cummings as Julie Arnold
Boris Karloff as Jim Henderson
Claude King as Arnold
Bertha Mann as Nurse Edwards
Edward Van Sloan as Dr. August Steiner / Dr. Alec Munsell / Mr. X