If I was on the jury in To Kill a Mockingbird, I'm sure I would have found Tom Robinson not guilty. Of course, this is exactly how the writer, Harper Lee, wants her readers to feel.
The novel is heavily biased in favor of Robinson. The accusers, the Ewells, are presented in such a negative light that it's impossible to sympathize with them. Robison, on the other hand, is a character that readers can feel for.
Also, the only hard evidence that was presented in the trial was the fact that Robinson was unable to use his left arm, and that Mayella Ewell was attacked by someone who used his left arm. Atticus was able to show that Mr. Ewell, Mayella's father, was left-handed, and very temperamental. Atticus hoped by this to shift suspicion away from Robinson to Mr. Ewell.
Other than that, it came down to a lot of he-said, she said. It was difficult for a black person to win a trial in the deep south in the 1930's based on that kind of evidence.
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