Lets start with the pre-trial. This demonstrates how firmly imbedded racism is in this community. Although the Ewells were not a respected family in Maycomb, no one doubts their story. Instead, the town rallies around them and shuns Atticus, a well-respected member of the community. Then, the "gang" appears at the courthouse to "take care" of Tom Robinson. This again demonstrates the strength and depth of racism in this community. While still respectful of Atticus, the group was ready to run him over in order to get at Tom Robinson.
During the trial, we see the segregation of the town that is a part of this racism. The black community is in the balcony, the white community on the floor of the courthouse. We see how ridiculous the Ewell story is, and see that racism is causing this town to accept the word of violent white father over that of a helpful and caring black man. However, there is a shining light. Because the jury takes so long to return a verdict, Lee shows that the town is slowly starting to change. In the past, a black man would have been instantly convicted on the word of a white man. Here, the town shows some character, and at least considers letting the truth and letting justice prevail.