Would anyone feel differently had he served his entire sentence? I don't think so.
He's been in prison since he was 16. He got a 40 year sentence instead of life, 'cause the family didn't want to have to deal with the ugly details in court. Yes, I know they're horrific, but the kid had to be a bona fide nutcase. And, at 16, his chances of still being alive in 40 (35 to date) years was pretty good and they had to know that then.
If he committed any crime in prison, it should have been tried and a new sentence added on, if he were found guilty. Same with sex offenders, or anyone.
If you're going to sentence someone to X # of years, it should not be possible, without further offenses, to extend that sentence just because we're afraid. We do that here in MA (here, Chris, Massachusetts). We've got a slew of sex offenders, levels 1-3, who have served all of their time and we're still holding them just because we feel like it.
Sure, it eases public fears, but the sentence you are remanded to serve is/was the law. It made no provisions for societal changes to incur add-ons.