Call Northside 777 (1948)

In Chicago in 1932, during Prohibition, a policeman is murdered inside a speakeasy. Frank Wiecek (Richard Conte) and another man are quickly arrested, and are later sentenced to serve 99 years' imprisonment each for the killing. Eleven years later, Wiecek's mother puts an ad in the newspaper offering a $5,000 reward for information about the true killers of the police officer. This leads the city editor of the Chicago Times Brian Kelly (Lee J. Cobb) to assign reporter P.J. McNeal (James Stewart) to look more closely into the case. McNeal is skeptical at first, believing Wiecek to be guilty. But he starts to change his mind, and meets increased resistance from the police and the state attorney's office, who are unwilling to be proved wrong. This is quickly followed by political pressure from the state capital, where politicians are anxious to end a story that might prove embarrassing to the administration. Eventually, Wiecek is proved innocent by, among other things, the enlarging of a photograph showing the date on a newspaper that proves that a key witness's statement was false.