How does the author of A Lesson Before Dying immediately set the novel's tone with the opening sentence?

Gaines begins the novel with these words:

I was not there, yet I was there. No, I did not go to the trial, I did not hear the verdict, because I knew all the time what it would be. Still, I was there.

What the narrator is talking about is the murder trial of a man named Jefferson. He is the proverbial person in the wrong place at the wrong time: He and two friends tried to persuade a store owner to give them a bottle of wine on credit. When the store owner refused and threatened them with a gun, one of Jefferson's friends fired his own gun. In a matter of minutes, the white store owner and two black men lay dead on the floor. The only person standing was Jefferson. The police immediately suspect him of being the shooter. He is arrested and given a speedy trial.

When the narrator, Grant Wiggins, says that even though he never attended the trial he was there all the same, he is setting a tone of futility and hopelessness that will be felt throughout the novel. He didn't have to be at the trial to know that Jefferson was going to be found guilty. The circumstantial evidence, plus the fact that a black man was unharmed while a white man lay dead, were enough to convict him. Add to that the fact that the jury was probably twelve white men, and what hope does Jefferson have? Grant didn't have to be present in the courtroom to know that any black man under the same circumstances would have been found guilty.