The Snorkel

A wealthy husband, Paul Decker, commits a gruesome murder in his Italian villa by drugging his wife's milk and asphyxiating her. He cleverly conceals himself in a hidden trapdoor and uses a scuba snorkel to breathe while the body is discovered by servants. The victim's stepdaughter, Candy, becomes suspicious of Decker and his dark past, which includes a potential murder of her father years prior. Despite her accusations, no one believes her, and Decker even goes to extreme lengths to silence her by poisoning the family pet.