12 Angry Men (1957)

Sidney Lumet’s 12 Angry Men is a landmark courtroom drama set almost entirely inside a jury room. As twelve jurors deliberate a murder case, one dissenting voice forces them to confront prejudice, doubt, and the meaning of justice. A tense, dialogue-driven classic, it remains one of the most influential American dramas of all time.

Från IMDB:
The jury in a New York City murder trial is frustrated by a single member whose skeptical caution forces them to more carefully consider the evidence before jumping to a hasty verdict.