In Alabama in the 1930s, this case should have been decided and over with before an hour was up. That should have been the case of Tom Robinson in this novel as well. However, what is odd about it is that we find that the jury is conflicted. They have seen the evidence (or lack thereof) and they know that the Ewells are lying. However, society has taught them to be prejudiced, and this should be a open/close case. It should be easy to decide. In a later chapter we find that Mr. Cunningham's relative was the one to keep them out so long. Of all people, the one man who brought his Sarum Bunch forward to harm Tom the night he was moved to the jail, Mr. Cunningham found respect for Atticus that night. So his family all look at Atticus a little differently now. That Cunningham was going to do what was right, rather than what society had taught him to do/believe. If Atticus could do right, by golly, so could the Cunningham family.
It depends who you ask about the predictability of the verdict. Every semester that I teach this novel I get ANGRY students. They honestly believe that Tom is going to be let go. He didn't do it. However, they are surprised (and angered). So I don't believe it's predictable. Part of us knows he'll be guilty. The other part prays that these people will do what's right. So we don't know until we read it.