This was Faye Dunaway's first movie.
The basic plot of this movie bears a striking resemblance to that of a minor British comedy of about eight years earlier, "Too Many Crooks", and was used again many years later for another American movie, "Ruthless People".
During this film's shoot, Robert Walker Jr. worked on another project at the same time. The second week of filming, he did double duty filming an episode of Au coeur du temps (1966), where he played Billy the Kid.
Roc Delmonico makes the first ransom calls from pay phones in front of the historic Houlover Lighthouse Restaurant in North Miami Beach. It was known for a large tank where guests could feed turtles. It burned down in December, 1967, a few months after the scene was filmed. The turtles did not survive.
A variation of the track "The Fuzz", played in the movie, is used as the opening of many TV news programs, including Jornal Nacional (1969), which is still in use after more than 50 years.