ON SCREEN: "This film was photographed in the State of Illinois using wherever possible, the actual locales associated with the story." This was the first Hollywood-produced feature film to be shot entirely on location in Chicago. Many famous landmarks, such as the Chicago Merchandise Mart, Holy Trinity Polish Mission, and the Wrigley Building (of chewing gum fame) on North Michigan Avenue, can be seen throughout the film.
The "roundhouse" where Wiecek is kept at the Stateville prison was the only remaining panopticon still in use in the United States in the 1990s. It was closed in 2016 but the structure remains due to its historical significance.
ON SCREEN: "THIS IS A TRUE STORY" Actually, this film was based on a true story. Some elements, especially characters names, were fictionalized out of necessity, such as some central figures to the story were still living at the time of production, and had not given permission for their names to be used.
James P. McGuire served as a technical advisor on this film. He is the Chicago Times reporter who wrote the articles on which this film is based and is the basis of the character played by James Stewart.
Thelma Ritter's role as the police captain's secretary was mostly deleted from the released print, but she can still briefly be seen and heard in one scene in which she tells James Stewart the captain will see him in his office.
The trivia items below may give away important plot points.
Frank's name in real life was Joseph Majczek. After being released from prison in 1945, he worked as an insurance agent in Chicago. For his wrongful imprisonment, the State of Illinois awarded him $24,000, which Majczek gave to his mother Tillie. Majczek eventually remarried his wife with whom he had divorced while he was in prison. His last years were spent in a mental institution; he died in 1983.
The man imprisoned with Frank/Majczek, Tommy, whose name in real life was Theodore Marcinkiewicz, was released from prison in 1950, five years after Majczek. Marcinkiewicz was awarded $35,000 from the State of Illinois for his 17 years of imprisonment.