I've been meaning to see this movie for a long time, and since it has now been re-released on DVD, I was at last able to. And I certainly don't regret it: I put Twelve Angry Men on my shortlist of all-time favorite films. This captivating huis clos (a mixed metaphor, perhaps, but descriptive), starring Henry Fonda as the dissenter, shows how a criminal jury, initially voting eleven to one for conviction (and death), come to be convinced by the dissenting juror.
I've often wondered how things really happen in the secrecy of jury rooms. I've so often seen how unmanageably difficult it is to secure any kind of agreement from a group of people, even on a subject utterly unimportant (many cases dealing with computers come to my mind), when some are convinced of what is Right and True and Good, that I can't imagine how twelve people ever manage to reach an agreement about something so grave as criminal matters, guilt and innocence. Actually, I wonder if demanding a unanimous verdict is such a good thing, because it might be the cause some bullying among jurors.
French and American procedure differ in important respects in this matter. For one thing, according to French law, the popular jury of nine jurors (or twelve in an appellate court, randomly drawn, as in the United States, and which the parties can challenge upon drawing) deliberates together with the three professional judges of the assize court: the same twelve (or fifteen) people make their verdict as to the defendant's guilt, for one, and the sentence in case of guilt (but no civil damages, which are the judges' decision only). I think this makes good sense. The deliberation, also, is very formal: as I understand it, agreement does not have to be reached, eight ballots (ten in an appellate court) are required to declare the defendant guilty, and if fewer votes are cast in favor of guilt, the court's ruling is innocent; the sentence is voted upon in order of decreasing severity, again requiring a majority of two thirds to approve a sentence. The legal rules are set out in articles 355 through 365 of the Code de Procédure pénale (English translation here).