Call Northside 777 (1948)

In 1932, Frank Wiecek (Richard Conte) is convicted of the murder of a Chicago policeman in a mob-connected speakeasy. Eleven years later, his mother, Tillie (Kasia Orzazewski), takes out a newspaper classified ad asking for information about the crime. Hard-bitten city editor Brian Kelly (Lee J. Cobb) assigns skeptical reporter P.J. McNeal (James Stewart) to investigate. The first studio feature ever shot on location in Chicago, the film is based on a true story.