Assume the role of Aunt Alexandra or Calpurnia. Tell Tom's story from that character's perspective, and explain in character, why you feel it right to defend or accuse Tom of raping Mayella.
Aunt Alexandra is a traditionalist who is also prejudiced against African Americans. We know that Aunt Alexandra disapproves of her brother defending Tom Robinson from Francis's interpretation of her comments regarding Atticus. In addition, the majority of Alexandra's peer group is also prejudiced against African Americans. Taking her social views into consideration, one would assume that Alexandra would support Tom Robinson's conviction, even if she believed that he did not rape Mayella. Similar to the jurors who knowingly convicted an innocent man, Alexandra would support the decision to convict Tom simply because of her prejudice. Alexandra is intelligent enough to figure out that it was impossible for Tom Robinson to inflict those injuries on Mayella. She also knows that her brother would only defend an innocent man. Since Alexandra is a traditionalist, it can be assumed that she would not be in favor of giving African Americans the same rights as white people. She more than likely realizes that Tom is innocent, but would not support an acquittal because of its inevitable social impact. Alexandra would say something along the lines of, "I have no reason not to believe that poor, white girl. You all know how dangerous Negros can be. I would not be surprised one bit if Tom Robinson beat and raped her."
Calpurnia would fully support Tom Robinson and defend his character throughout the trial. Calpurnia is a close friend of the Robinson family and knows that he would never take advantage of Mayella Ewell. She is also aware of the Ewells's reputation throughout town and would know they are lying on the witness stand. She would more than likely recognize Mayella's contradictions immediately and take into account the fact that Mayella's father had the motivation to assault her. Calpurnia would also understand that Tom is physically incapable of inflicting those injuries upon Mayella. Calpurnia would argue for Tom's acquittal at the end of the trial.