What are some comparisons that Mr. Underwood makes about Tom's death and trial in To Kill a Mockingbird?

Several days after the prison guards killed Tom Robinson, B. B. Underwood wrote an editorial in The Maycomb Tribune. One key phrase that Scout picks up on is “senseless slaughter.” Scout notes that Underwood had referred to Tom as a “cripple”—a term that formerly was frequently applied to people with disabilities—and she initially assumes that his criticism is directed toward the guards because they shot a partially disabled person, which would be wrong whether that person was “standing, sitting, or escaping.” What prompts Scout to analyze the editorial further, however, is Underwood’s use of “slaughter” along with “hunters and children.” In this regard, Underwood is not only comparing the guards to predators and Tom to animal prey but also judging the guards’ actions as childish. Tom, in his estimation, resembles a “songbird.” While Underwood strongly criticizes the guards’ action, he avoids discussing the trial, and he explicitly omits any discussion of race. Scout makes those connections on her own.

In chapter 25, Scout mentions that the citizens of Maycomb were interested in the news of Tom's tragic death for two days before they forgot about it. However, Scout recalls reading an article written by Mr. Underwood in The Maycomb Tribune in which he expressed his displeasure and disgust at Tom Robinson's tragic death. Scout mentions that Mr. Underwood did not elaborate or speak on miscarriages of justice and simply believed that it was a sin to kill "cripples." In the article, Mr. Underwood likened Tom Robinson's death to the senseless slaughter of songbirds at the hands of merciless hunters.
Mr. Underwood's analogy directly corresponds to Atticus's lesson regarding the importance of protecting innocent, defenseless beings when he explains to his children that it is a sin to kill a mockingbird in chapter ten. After reading Mr. Underwood's article, Scout finally understands its meaning and mentions,

Atticus had used every tool available to free men to save Tom Robinson, but in the secret courts of men’s hearts Atticus had no case. Tom was a dead man the minute Mayella Ewell opened her mouth and screamed. (Lee, 245)