The dissenter is Henry Fonda, and gradually he convinces the other eleven, not that the accused is innocent (they don't know that), but that he - like everyone - should get a fair trial and that the evidence is full of holes. In other words, there is plenty of room for a "reasonable doubt." In the process, every jury member is shown as an individual character, whose background may be pushing him to take a certain stance. The story comes neatly full circle, but it is a bit too neat, "Hollywood-style," and the prosecutor's work is shown as just too sloppy (not to talk about the defense) to be realistic.
Anyway, I am glad I am not living in a country with a jury system. Seeing the flimsy grounds on which most of the jurors decide (personal prejudices) does not inspire confidence in such a system. It is only a more civilized form of lynching. If Fonda would not have held out against eleven others - most people would have gone along with such an overwhelming majority - and patiently argued the case with the "angry men," the accused would have been wrongly executed.
It is interesting to watch the cultural traits in this film: the body language, the fact that these American (Western) men simply can't sit still, and also have trouble concentrating - but in the end, they do get the job done. They all have clear opinions and state these loudly and confidently. The discussions are rather confrontational. One of the men acts as chairman (of course, as is usual in A,merica, his authority is challenged at a certain time - leaders have to prove themselves all the time), but the whole process is quite disorderly. I realized how used I am to more quiet and orderly processes because of my life in Japan. When in a meeting, Japanese don't get up to pace the room all the time, the discussions would be more polite and general procedure would be more structured. But whether that means the job would be done faster, I don't know... (although it would be done in a more pleasant atmosphere).
12 Angry Men is worth watching for these cultural traits - there is also excellent acting all-around the table, and the story satisfies as the "good guy" (Fonda, who uses both his mind and his heart) wins. But this film is not the great plea for democracy some people have made out of it, on the contrary, it only shows how dangerously fallible the jury system is.
Twelve Angry Men is available in the Criterion Collection.(Revised August 2014)