Harper Lee's subplot of the arrest and trial of the compassionate and gentle African-American Tom Robinson is loosely based upon the legal cases connected to what have been called the cases of The Scottsboro Boys in 1931 (the incident occurred in Scottsboro, in northern Alabama). The incident began after white male teens jumped off a train on which they had been hoboing. They went to the sheriff, accusing the African-American male youths who were also on the train of attacking them. The sheriff stopped and searched the train at another town. The African-American males were arrested. More damaging, two white women, who were also on the train, descended from the same train car and accused the blacks of rape. The women placed blame upon the African-American males because they had been seen in the company of these men. One of the women later dropped the rape charges and admitted that nothing had occurred between the women and the African-American males. The trials of the nine African-American men, then, involved issues of the right to a fair trial and racism since no black jurors were allowed in the Jim Crow South. In addition, there were disruptive mobs and rushed trials. This historical incident stands as an example of miscarriage of justice in the United States legal system.
Therefore, since To Kill a Mockingbird is set in the 1930s and in Alabama, the parallels between Harper Lee's depiction of Tom's trial and the actual trial of the Scottsboro Boys point to the racism and injustice present in the setting.