Why does Lee select a Cunningham to be the juror who cast the non-guilty votes?

Walter's dad had a revelation of sorts. It took the innocence of a child (Scout) to snap him out of his ignorance. When the mob cornered Atticus, Scout gently reminded him what he was doing. In the end Cunningham had racial bias but he was still a fair man who knew right from wrong. Lee wanted to have us remember that people can change.