So are you saying that some of those found guilty are DEFINATLY guilty and can be put to death, while others are guilty but with reservations, and can be imprisoned but not hung (or whatever cruel and unusual punishment the sun-readers-brigade are hoping for this morning). At the end of a trial, the jury have to decide between guilty and innocent. There isn't a 'definately' guilty and 'probably' guilty area. If the jury find you guilty, you get whatever sentence the law and the judge allow, and if that is a death sentence, then it will apply to everyone, not just monsters like Huntley. If you think you can create a law which divides different sorts of levels of probable guilt and see it upheld in front of lawyers and a judge, you're a better man than I am.
At a personal level, I am a father of two girls and the idea that Huntley and other *****philes continue to live and breathe is repellant to me, but we are trying to make a civilised society, and a death penalty would almost certainly not have deterred Huntley, nor brought the two girls back to life. I certainly don't think the man should ever walk free again, and (if this is true), the money he is claiming in damages for a prison attack should go to the girls family in compensation or to the prison services to continue feeding him, but the death penalty while probably deserved is not a solution.
Sorry to be so long winded, you touched me on a nerve! ;-)