For what reasons is juror eight uncertain about the defendant's guilt in Twelve Angry Men?
When the first juror poll is taken, Juror Eight votes "not guilty." When challenged, he just says that he doesn't think the accused is necessarily guilty or not guilty, just that he thinks a man's life is worth a little discussion. If the jury is to condemn this men as a murder, he reasons, they should spend a little time on the decision and honor the fact that what they are doing is serious and significant. Only later does Juror Eight start to raise solid questions about the crime's time frame, the knife, and the witness testimony.
This relates to a major theme of the play, that is that justice can only be served if honest (wo)men are willing to see that it is implemented responsibly.