What is the relationship between B.B. Underwood's editorial and the book's title, To Kill a Mockingbird?

Earlier in the novel, Atticus points out that
The Maycomb Tribune editor, B. B. Underwood, "despises Negroes,
won't have one near him." Yet, it is Underwood who silently stands guard at his office
next to the jail on the night the lynch mob comes to confront Atticus and take Tom
Robinson. In his editorial following Tom's death, Underwood refers to several aspects of
the title of the novel. The title, based on Atticus' reminder to Jem after having
received an air rifle for Christmas, that it's "a sin to kill a mockingbird," refers to
the innocence of the bird (and the symbolic human mockingbirds within the story).
Underwood picks up this theme in his editorial, likening "Tom's death to the senseless
slaughter of songbirds by hunters and children."