Atticus's decision to take the case at the insistence of Judge Taylor is his first step in seeing that Tom receives a solid defense. Atticus tells his brother Jack that he hopes to "jar the jury a bit" and that their best chance will be on appeal. During his questioning of Sheriff Tate, Atticus establishes that there were no witnesses to the altercation between Tom and Mayella except for Bob Ewell; that Mayella was never treated by a doctor; that she was "beaten around the head...all around her throat"; and had a blackened right eye. Atticus determines that Bob Ewell is a racist (he calls Tom "that black nigger yonder") and that he is left-handed.
From Mayella, Atticus shows that she, too, is a racist (also referring to Tom as a "nigger"); that her testimony is unreliable (she repeatedly changes her story); that she is not certain if Tom hit her (though she later claims that "He done what he was after"); that Bob was not "tollable" when he had been drinking; that Tom had been on the Ewell property before; and that the crippled Tom had beat her.
Atticus's questions to Tom provide him with the opportunity to give a truthful account of the attack. Tom tells the jury that Mayella invited him inside the house; that she first hugged and then kissed him; and that Tom ran away afterward. During his summation to the jury, Atticus reminds the men that Tom's crippled arm prevented him from creating the bruising around Mayella's neck; that the Ewell's testimony should "be called into question"; that Mayella is guilty of having "tempted a Negro"; and that Tom was a "quiet, respectable, humble Negro" who was only charged with the crime because of his skin color.
Atticus tried to convince Tom to remain hopeful since there was a "good" chance that Tom could be freed on appeal, but Tom's decision to try and escape--because he was "tired of white men's chances and preferred to take his own"--ended in his death.