In Chapter 30, Sheriff Tate and Atticus discuss Bob Ewell's attack and death. Initially, Atticus believes that Jem was responsible for killing Bob. Sheriff Tate then explains to Atticus that Jem did not kill Bob. He says that Boo Radley was simply preventing a crime from being committed. Tate then tells Atticus that he refuses to inform the citizens of Maycomb about Boo Radley's heroics because it will bring unwanted attention to Boo's doorstep. Tate says that he would be doing Boo a disservice by forcing him into the limelight and considers it a sin. When Atticus looks down at Scout and asks her if she understands, Scout says,
"Well, it'd be sort of like shootin' a mockingbird, wouldn't it?" (Lee 169).
Throughout the novel, mockingbirds symbolize innocent beings. Earlier in the story, Atticus teaches Jem and Scout about the importance of protecting and respecting innocent beings. Scout metaphorically applies Atticus' lesson about not shooting mockingbirds to Boo Radley's situation in Chapter 30. Sheriff Tate refuses to harm an innocent being by exposing Boo Radley's heroics to the community. Tate's actions connect to both the theme and title of the story.
At the beginning of Chapter 25 of To Kill a Mockingbird, Jem catches Scout about to smash to death a "roly-poly"--better known as a "pill bug" or "doodlebug." The bug was not bothering Scout, nor is it particularly harmful to other living things. About an inch long, the roly-poly rolled itself into a ball when Scout approached it. Jem ordered Scout to stop and
"... set him out on the back steps."
Scout thought Jem was crazy, and she asked him why she shouldn't mash it.
"Because they don't bother you," Jem answered...
Like the mockingbird, the roly-poly was an innocent and harmless creature. Since this scene immediately follows Tom Robinson's death, Jem is still reeling from the knowledge that this poor, innocent man was dead.