In this scene Heck Tate is trying to convince Atticus to go forward with the story that Bob Ewell was killed by falling on his knife. At the beginning of the scene, Atticus believes that his son Jem did the killing because of the way Scout describes the scene. Atticus is actually misunderstanding Heck’s intention at first, thinking that he wants to shield Jem from the stigma of having to face the legal process of explaining the killing in court.
Atticus definitely believes what he’s saying. He is motivated by his desire to be a good role model for his children. At one point he says,
“If they hear of me saying downtown something different happened—Heck, I won’t have them anymore. I can’t live one way in town and another way in my home.”
He also wants to prevent them from facing a future of public suspicion over how this event was handled legally. He figures facing the truth now is the best way. Atticus says,
“I don’t want anybody saying, ‘Jem Finch . . . his daddy paid a mint to get him out of that.’ Sooner we get this over with the better.”
Finally, Heck gets through to Atticus and forces him to see what he really means: “God damn it, I’m not thinking of Jem!” In other words, he’s thinking of Boo Radley. Heck believes Boo killed Bob Ewell to protect the kids. He also believes that all the attention of the killing would be torture for Boo.
Heck does not believe his own story because he is making it up to protect Boo. He does believe that it’s the right thing to do however. He expresses this thought with a biblical allusion:
“There’s a black boy dead for no reason, and the man responsible for it’s dead. Let the dead bury the dead this time Mr. Finch.”