The main facts that prove that Tom Robinson has been falsely accused in To Kill a Mockingbird are that Bob Ewell did not call a doctor for Mayella and there is no proof the crime was committed, Bob Ewell is left handed, and Tom Robinson’s left hand is crippled.
First of all, Atticus goes to great pains to establish the inconsistencies in both Mayella and Bob Ewell’s stories. Clearly they are both lying. First of all, Ewell says he saw Tom Robinson rape his daughter, but he never called a doctor. No one did.
"Well I can tell you why I didn't. It wasn't necessary, Mr. Finch. She was mighty banged up. Something sho' happened, it was obvious." (ch 17)
If Mayella had really been attacked by someone other than her father, her father should have called a doctor. He didn’t call a doctor because he didn’t want too many people asking questions. A doctor would have revealed that Mayella had not been raped.
Second, Atticus also demonstrates that Mayella was beaten up on the right side of her face, and Bob Ewell is right handed. Heck Tate testifies that the right side of Mayella’s face was beaten.
"'Mr. Finch. I remember now she was bunged up on [the right] side of the face.'" (ch 17)
For a person to be hit on the right side of the face, the person who attacked must be left handed.
If her right eye was blacked and she was beaten mostly on the right side of the face, it would tend to show that a left-handed person did it. (ch 17)
This is important forensic evidence. Jem is quite convinced that there is no way that Tom Robinson can be convicted, since Bob Ewell is left-handed.
Finally, Tom Robinson’s left hand is crippled, so he could not have attacked Mayella on the right side of her face.
His left arm was fully twelve inches shorter than his right, and hung dead at his side. It ended in a small shriveled hand, and from as far away as the balcony I could see that it was no use to him. (ch 18)
In the end, it does not matter that there was no proof that the crime Tom Robinson is accused of was ever committed, that Bob Ewell beat his daughter, or that Tom Robinson is crippled. Robinson is convicted because he is a black man accused by a white woman.