Boo Radley is one of the human mockingbirds of the Harper Lee novel, a man who is mocked by town rumors and accused of crimes he did not commit. It is Atticus who warns Jem that "it's a sin to kill a mockingbird," and Miss Maudie later explains to Scout that
"Mockingbirds don't do one thing but make music for us to enjoy. They don't eat up people's gardens, don't nest in corncribs, they don't do one thing but sing their hearts out for us. That's why it's a sin to kill a mockingbird."
Lee uses the mockingbird as a symbol of beauty and innocence. They become silent when death approaches, as in the case of Atticus' killing of the mad dog. The "mockingbirds were still" as the jury pronounced the innocent Tom Robinson guilty, and his death is likened to "the senseless slaughter of songbirds" in the newspaper editorial. A mockingbird warns the children that danger is near on the night of the Halloween pageant, and it is Scout who later tells her father that exposing Boo to the public scrutiny of an investigation into Bob Ewell's death would
"... be sort of like shootin' a mockingbird, wouldn't it?"
Along with Tom and most of the children in the novel, Boo is like the mockingbird: a peaceful innocent who is nonetheless the occasional target of citizens armed with misguided gossip and innuendo.