Well, I don't quite understand at which point you were given the right to decide whether someone lives or dies, could you clarify for me? Why should someone like you stop someone like this from getting several years in a good rehabilitation program and a second chance at life? Just because it makes you feel safe, it doesn't solve the problem.
Locking someone away for 15-20 years and then releasing them and expecting them not to reoffend rarely works for any crime. The same is true for putting them on a register, giving them curfews, and most of the other penalties that they receive. Rehabilitation is what works.
This idea you have that sex offenders will carry on committing offences of a sexual nature once released shows how little you know about the subject. They respond to treatment as well as any other criminal group, and are certainly not a lost cause to be cast away.
Oddly enough, the less you isolate and punish sex offenders, the less likely they are to reoffend. This is true for all criminals.
EDIT: Oh, and Johnny, please stop. Next you'll have us stamping all our posts with "Just my opinion". Being upset at a story as tragic as this is no justification for typing out some very sick wishes. If anything, it is an insult to the victim, as you are doing nothing to fix the problem.