What does mr. underwood mean about tom's death?

In his editorial Mr. Underwood calls Tom's death a "senseless slaughter of a songbird"; this of course ties directly into the title of the novel. Tom is an innocent mockingbird killed by ignorance, injustice and bigotry. Mr. Underwood is a man who lives by his own rules. Printing this, however, puts his business and himself in jeopardy. Mr. Underwood feels very strongly about this travesty of justice.