Claude Chabrol announced this project several times in the 1960s, always naming Orson Welles for the role of Theo Van Horn, but at various times mentioning Tom Courtenay and Catherine Deneuve (amongst several others) for the roles finally taken by Anthony Perkins and Marlène Jobert. It was always the unavailability of Welles which led to the several postponements of the filming, and the re-casting of the other leads. When asked why he did not simply hire another actor to play Theo, Chabrol replied, "Only Orson Welles can play God."
Although this film is based on one of the most renowned of the Ellery Queen detective novels, it removes entirely the character of Ellery Queen.
Although filmed in France by an essentially French team, the film was shot entirely in English. Orson Welles is dubbed in French by Georges Aminel and Anthony Perkins by Philippe Nicaud, despite Perkins relative mastery of the language, proved in Agent 38-24-36 (1964).
It is said that Claude Chabrol chose Alsace as the location for Ten Days Wonder (1971) simply because he wanted to sample the local cuisine.