In an interview for the Dutch Filmkrant, Fons Rademakers said that he doggedly pursued Orson Welles for a full year to sign him up for a role in the movie.
Based on a novel by Nicolas Freeling in the 'Van der Valk' series.
Sylvia Kristel revealed that the nude swimming scene was very difficult to film. "It was February and the temperature was 40 degrees below freezing. I had to walk into the North sea, very gracefully, I must say. There were six other girls in the shot and they all fainted. But not me," she said.