"The Killer Must Kill Again" (original Italian title: L'assassino è Costretto ad Uccidere Ancora), also known as The Dark Is Death's Friend, is a 1975 Italian giallo film directed by Luigi Cozzi. This suspenseful thriller showcases the distinctive elements of the giallo genre, combining murder mystery with psychological horror and stylistic flourishes.

The film's narrative centers around Giorgio Mainardi, played by George Hilton, a financially troubled man who orchestrates the murder of his wife by hiring a cold-blooded killer, portrayed by Michel Antoine. However, the plan takes an unexpected turn when the murderer's car, with the corpse inside, is stolen by two young lovers, Luca (Alessio Orano) and Laura (Cristina Galbó), who are unaware of the gruesome cargo they are transporting.

As the story unfolds, the killer embarks on a relentless pursuit to retrieve the evidence and eliminate anyone who might expose him, leading to a series of tense and violent encounters. The plot weaves through a web of deception, betrayal, and escalating terror, keeping the audience on edge with its twists and turns.

Cozzi's direction is marked by a meticulous build-up of suspense and a keen eye for visual style, characteristic of the giallo genre. The film features striking cinematography, with vivid colors and dramatic lighting that enhance the eerie and menacing atmosphere. The haunting musical score by Nando de Luca further amplifies the tension and mood.

"The Killer Must Kill Again" is notable for its intricate plotting and psychological depth, exploring themes of guilt, desperation, and the dark impulses that drive people to commit unspeakable acts. The performances by the cast, particularly Hilton and Antoine, add to the film's compelling and unsettling narrative.

Overall, "The Killer Must Kill Again" stands out as a gripping and stylish entry in the giallo genre, showcasing Luigi Cozzi's talent for crafting a chilling and engaging thriller that continues to resonate with fans of Italian horror cinema.