Producer Horst Wendlandt kept the last pages of the screenplay in a safe and had each of the leading actors sign a special insurance document in order to keep the surprise ending a secret.
The Scotland Yard man at Gwenda Milton's funeral, sitting and reading on a bench, is reading "Little Women".
The title/credits sequence is in full color. The pre-title sequence and the rest of the film is in black and white.
In this version, the Inspector's name is Bryan Edgar Higgins. Bryan Edgar Wallace was the name of Edgar Wallace's son who was also a writer of thrillers, including some of these German "krimi" features. He passed away in 1971.
This was based on a novel by Edgar Wallace that was also known as "The Gaunt Stranger". It was adapted into a play. There had been three previous British film adaptations. There had also been an earlier German feature film released in 1932.