Who killed Bob Ewell?
Boo Radley wrestles Bob's knife out of his hands and ends up killing him.
In chapter 28, Bob Ewell attacks Jem and Scout as they are walking home from Maycomb's Halloween festival. During the attack, Scout cannot identify the person wrestling Bob Ewell off of her and Jem because her ham costume obstructs her vision. After the scuffle ends, Scout sees the outline of a man walking with staccato steps carrying Jem home. When Scout returns home, she meets Boo Radley for the first time as Atticus and Sheriff Tate discuss who killed Bob Ewell. Atticus initially believes that Jem killed Bob Ewell, but Sheriff Tate disagrees. Sheriff Tate then tells Atticus, "Bob Ewell fell on his knife. He killed himself" (Lee, 277). However, Atticus insists that his son take responsibility for murdering Bob Ewell. Sheriff Tate then demonstrates how Bob fell on his own knife before indirectly telling Atticus the truth. Sheriff Tate admits that Boo Radley stabbed and killed Bob Ewell with a kitchen knife by telling Atticus,
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 [Boo Radley] 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 [Boo Radley] 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. If it was any other man, it’d be different. But not this man, Mr. Finch (Lee, 280).
The man Sheriff Tate is referring to in the previous quote is Boo Radley, who is the most reclusive citizen in Maycomb. Sheriff Tate refuses to tell the community about Boo's heroics in order to prevent Boo from stepping into the community's limelight. Sheriff Tate then tells the community that Bob Ewell simply fell on his own knife and died.