I think that Tom Robinson's death is the very embodiment of injustice. Atticus himself points this out when he suggests that the jury and the town embrace "the evil assumption . . . that all Negroes are basically immoral beings." This represents the basic injustice that governs Tom Robinson's life as well as the lives of all African- Americans in the South of the time period. Tom experiences injustice in the fact that he is automatically presumed guilty because he is a man of color in a word stratified by race. Such a condition embodies injustice.
Tom being imprisoned is a reflection of this injustice. When Tom is killed by the guards, it represents injustice because he should never have been imprisoned in the first place. The setting that brings about his death should not have been a place in which he existed. The fact that he was shot 17 times under the cover of needing to restore order in response to him escaping is another example of injustice. When Tom tells Scout at the end of the novel that most people are [real nice] "when you see them," it is a stinging reminder that the death of Tom Robinson represented the essence of injustice. Tom was never "seen" by those in the position of power. He was never seen as a human being. In this, the injustice that envelops his life and brings about his death is most evident. Tom's sense of goodness was never validated. He never received due credit for helping someone who needed it, expanding his sense of compassion and empathy. Instead, he experienced scorn and rejection, and in the process died a death rooted in injustice.