Towards the end of chapter 30, Sheriff Tate and Atticus discuss who murdered Bob Ewell. Sheriff Tate knows that Boo Radley ending up killing Bob Ewell during the struggle to save Jem and Scout but does not initially bring it up during his conversation with Atticus. However, Atticus believes that his son is responsible for Bob's murder and argues with Sheriff Tate when he says that Bob fell on his own knife. Atticus knows that Sheriff Tate is covering up the true nature of Bob's death and is convinced that Jem is responsible for killing Bob. When Atticus says that he refuses to cover up Jem's involvement in Bob's death, Sheriff Tate interrupts Atticus by saying,

God damn it, I’m not thinking of Jem! (Lee, 278).

Sheriff Tate wins the argument for several reasons. Sheriff Tate has ample evidence to argue that Jem could not have wrestled and fatally wounded Bob with a broken arm in the dark. He also has solid proof that Bob tripped and fell on his own knife. Furthermore, Sheriff Tate tells Atticus that he is willing to call him a liar to his face if he chooses to argue that Jem killed Bob. Most importantly, Sheriff Tate indirectly informs Atticus that Boo Radley was the person responsible for killing Bob Ewell by saying,

I never heard tell that it’s against the law for a citizen to do his utmost to prevent a crime from being committed, which is exactly what he did, but maybe you’ll say it’s my duty to tell the town all about it and not hush it up. Know what’d happen then? All the ladies in Maycomb includin‘ my wife’d be knocking on his door bringing angel food cakes. To my way of thinkin’, Mr. Finch, taking the one man who’s done you and this town a great service an‘ draggin’ him with his shy ways into the limelight—to me, that’s a sin. It’s a sin and I’m not about to have it on my head (Lee, 280).

After grasping the reality of the situation, Atticus stops arguing with the sheriff and respects Heck Tate's decision to protect Boo Radley from receiving unwanted attention from the community. 

After Bob Ewell is killed, Atticus and Heck Tate argue over how to handle the situation. Scout thought that Jem pulled Bob Ewell off of her and from this information, it is possibly that Jem may have stabbed Bob. Because Atticus is a model of honesty and integrity, he wants this event, trial and everything, to be out in the open. He doesn't want any suspicious thoughts (in Jem's mind or in the minds of others in town) to linger. Atticus just wants to do the right thing. What Atticus didn't, at first, understand is what Boo's role was in all of this and what an investigation might do to Boo.

However, Heck Tate realizes that is was more likely that Boo Radley was the one who...