What specific evidence did Atticus Finch use in the courtroom to prove Tom Robinson's innocence?

Atticus first gets Heck Tate's testimony from the investigation he did on the night in question. Tate reports that Mayella Ewell was "all bunged up" on the left side of her face. Atticus asks whose left, and Tate says his left, meaning it was on the right side of Mayella's face. Next, Bob Ewell, Mayella's father, takes the stand. Atticus asks him if he agrees with Tate's description of Mayella's condition, and he agrees. Then he asks if he can read and write; when Ewell says yes, he has him write his name in the full view of the court, thus demonstrating that Ewell is left-handed. When Mayella identifies Tom Robinson as her attacker and Atticus has him stand, the court sees that his left arm is shriveled, a full twelve inches shorter than his right. Reverend Sykes explains to Jem that he'd gotten the arm caught in a cotton gin when he was a boy and had been disabled since.