Let's be pragmatic...
What is to sin? Why forgive ?
Not clear.
A human adult kills a human child.
It's not about forgiveness.
It's about understanding why it happened, what could have been done to prevent it and apply what has been learned.
If it's still not good, cry it loud, be heard, argue.
What happens to the culprit is less important (and by itself won't prevent others from doing it anyway) than the measures taken to avoid the next kidnapping. It's a matter of quick reaction, spreading the information through most existing media.