How do the final events of the conclusion bring the two stories of the trial of Tom Robinson and the mystery of Boo Radley together?

After Tom Robinson was convicted and was killed trying to escape, it seemed like things were back to normal.  Scout was to perform in a play.  On the way home she was attacked by Bob Ewell.  He attacks Scout to get revenge on Atticus for the way he and his daughter were cross examined in court during the Tom Robinson trial.  After the attack it is Boo Radley that carries Jem home.  Scout finally gets to meet Boo and decides he is not scary at all.  Throughout the novel Boo is watching the children and in someways protecting them.  He fixes Jem's torn pants earlier in the novel. He leaves gifts in the tree for them, and in the end he saves Jem and Scout by killing Bob Ewell.  This is in someways a redemption for Tom Robinson.  The idea that what comes around goes around is really proved true here.  Ewell lies in court, and that is what helped convict Tom Robinson, so in the end he pays for his evil by giving up his life.