All you need to do is focus on juror 10. He is by far the most biased and prejudiced person in the play. He says:
We don't owe him a thing. He got a fair trial, didn't he? You know what that trial cost? ....Look, we're all grown-ups here. You're not going to tell us that we're supposed to believe him, knowing what he is. I've lived among 'em all my life. You can't believe a word they say.
"I don't understand...Look, you know how those people lie...They don't know what the truth is....Human life don't mean as much to them as it does to us...Look, these people are drinking and fighting all the time, and if somebody gets killed....They don't care."
If we examine these quotes two points of prejudice emerge. First, he generalizes the poor. He even says that because he lived among them, he knows what they are all like. They cannot be trusted. It does not take an intelligent person to know that you cannot make sweeping generalizations.
Second, notice his inconsistency. He calls those who live in the slum "them." If he lived among them, then can juror 10 be trusted? And why does he remove himself from them? In short, he is blind.