I have recently watched this movie and now I can't decide whether the boy was guilty or not. As per the proofs and evidences, he was guilty, but did the 8th juror's logic and countermeasure favour him?
We're never told either way. The movie is more focused on prejudice than anything else, and how some jurors wanted him to be guilty based on his background. In the end, a reasonable doubt is planted in everyone's minds, and according to jury instructions that reasonable doubt must result in a NOT GUILTY verdict, however no conclusive evidence is ever given as to the defendant's true guilt or innocence.
The first thing we should remember is the Judge's dialogue when he directs the Jurors.
Judge: To continue, you've listened to a long and complex case, murder in the first degree. Premeditated murder is the most serious charge tried in our criminal courts. You've listened to the testimony, you've had the law read to you and interpreted as it applies in this case, it's now your duty to sit down and try to separate the facts from the fancy. One man is dead, another man's life is at stake, if there's a reasonable doubt in your minds as to the guilt of the accused, uh a reasonable doubt, then you must bring me a verdict of "Not Guilty". If, however, there's no reasonable doubt, then you must, in good conscience, find the accused "Guilty". However you decide, your verdict must be unanimous. In the event that you find the accused "Guilty", the bench will not entertain a recommendation for mercy. The death sentence is mandatory in this case. You're faced with a grave responsibility, thank you, gentlemen.
Here, the Judge clearly defines the implications of "GUILTY" and "NOT GUILTY" whereby comes the most important phrase in this movie "REASONABLE DOUBT". As conclusively there was a reasonable doubt, therefore the boy was not guilty because the jurors had to abide by the definition supplied by the Judge