The Snorkel (1958)

Jacques Duval devises a fiendishly clever method of murdering his wife. Doping her up with sleeping tablets, Duval places his wife in a sealed room, then opens all the gas jets. While the police identify the body, Duval remains hidden in the room, breathing through a snorkel, then makes his escape when the authorities leave. Only one flaw in this perfect crime: Duval’s stepdaughter (Mandy Miller) is the suspicious type.
Guy Green
Peter van Eyck, Betta St. John, Mandy Miller, William Franklyn, Marie Burke, Irene Prador, Henri Vidon, Flush, Grégoire Aslan
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