In actuality, the only reason that any issues, any doubts are raised about the trial is because of one man, played by Henry Fonda, who almost immediately is of the opinion that the teenager is not guilty. This is a source of chagrin to most of the other jurors, who would much rather be anywhere else at this moment. One of them gets upset because he doesn't want to miss the ball game that he has tickets for. It is clear that many of the jurors just want to vote "guilty" right away so they can get the hell out of here. But Fonda puts a wrench in it, big time.
Fonda's character picks out all sorts of things that do not seem right to him. For one thing, the knife allegedly used for the murder: it was said that the knife that the kid had was rare, that hardly anyone would have a similarly designed weapon. But.... then Fonda reaches in his pocket, and pulls out a knife exactly like that of the teenagers'. So obviously, there is more than one of these knifes to be found in the city. Later on, Fonda questions the testimony of an elderly neighbor who supposedly ran to the door and saw the suspect running down the stairs. Fonda wonders how long it would take an old, slow-walking man to get to the door. The old man says that it was about ten seconds, so Fonda attempts to recreate the situation in the jury room. Fonda soon has a substantially different figure in mind.
These scenarios and more are Fonda's way of attempting to show that this supposedly open-and-shut case is not so simple. He attempts to convince them, one by one, that the teenager can't be found guilty, because there are too many doubts about all the crucial evidence.
