The last few paragraphs of the book are devoted to the victims of Patrick Sonnier, the teenagers Loretta Bourque and David LeBlanc. David's death is compared directly to "Jesus agonizing before he is led to execution" (11.154). In the final paragraph, Prejean talks about Lloyd LeBlanc, David's father, and how he forgave Sonnier but still struggles with feelings of anger and hatred. This is especially the case on David's birthday every year, as Lloyd thinks about how David would be growing up, becoming "a man like himself, whom he will never know" (11.157).
It may seem like an odd choice to end a book about the death penalty by talking about the irreparable harm caused by the executed man. But Prejean chooses the ending carefully. In the first place, she is pointing out that the grief Sonnier caused is not undone by his execution—in fact, it cannot ever be undone. Killing Sonnier doesn't bring David back to life. It doesn't heal anything.
Second, Prejean ends very deliberately with Lloyd LeBlanc because he is determined to forgive. He didn't wanted Sonnier to die, and he did not look to the justice system for revenge. Prejean, throughout the book, tries to campaign against the death penalty without forgetting the victims of crime or minimizing their pain. The end of the book is devoted to the victims because she doesn't want them to be forgotten.
And part of the reason she doesn't want them to be forgotten is because Christianity says you should not forget victims. Jesus was a victim, after all. He forgave his torturers, and that's what Christians like Lloyd LeBlanc struggle to do as well.
Finally, by focusing on the fact that the harm done by killing the teenagers has been absolutely, totally irreparable, Prejean highlights the fact that all killing results in catastrophic consequences that can never be fixed. This applies to the victims as well as to their executed murderers. In Prejean's view, there is no human or institution that can kill with impunity.