1. Following Atticus's comment about it being a sin to kill a mockingbird, there are several motifs regarding mockingbirds found throughout the novel. After Tom Robinson is wrongly convicted, he is sent to Enfield Prison Farm, where he attempts to escape. Unfortunately, Tom is shot dead during his escape, and Mr. B. B. Underwood compares his death to the "senseless slaughter of songbirds." Tom Robinson is a symbolic mockingbird because he is harmless and defenseless and only brings joy to the world.
2. In chapter 28, Jem and Scout walk to the Maycomb school to participate in the Halloween festivities. As they walk past Boo Radley's home, Scout mentions,
"High above us in the darkness a solitary mocker poured out his repertoire in blissful unawareness of whose tree he sat in, plunging from the shrill kee, kee of the sunflower bird to the irascible qua-ack of a bluejay, to the sad lament of Poor Will, Poor Will, Poor Will" (Lee, 258).
This specific mockingbird motif foreshadows Bob Ewell's attack on the innocent, vulnerable children as they are walking home.
3. The final mockingbird motif takes place at the end of chapter 30 when Scout metaphorically applies her father's lesson to Boo Radley. When Sheriff Tate says that it would be a sin to inform the community about Boo's heroics, Scout tells her father,
"Well, it’d be sort of like shootin‘ a mockingbird, wouldn’t it?" (Lee, 281).