This is a battle between reasons & emotions, self conscience & personal prejudice, life & death. Their "reasonable doubt" manifests basic respects for life and the protection against abuse of individual right & freedom under the judiciary system in a democracy.
Without flashbacks, the 12 men replayed the story simply by intercutting narration, and then contributed a vivid education about personal prejudice, legal system, and the spirit of democracy. Though bit theatric, the textbook group directing grips all dynamics and tension.