I have read over and over in the Catechism about the death penalty. The Catechism states that we have the right to protect ourselves and that means that in some cases that some persons have to be executed to protect society.
http://www.catholic.net/rcc/Periodicals/Dossier/9-10-98/article.html This guy is so sick that there is no way to protect anyone from him. Further, the longer he lives the more likely he will give rise to copy-cat killers and others who will try to emulate him. We have examples of this with Charles Manson, John Wayne Gacy, and Ted Bundy.
The real problem is that these death penalty cases are drug out for decades before the sentence is carried out. Whether or not the person is innocent or not is a big problem. Most of the people I have heard of who have been falselly accused were caught in the middle of comitting another crime like robbing a liquor store or rape; so these people weren't entirely innocent of any crime or wrong doing. But in his case he admitted to raping, killing and planning to eat this innocent little girl.
Let's not forget the victims of these abominable people who do these kinds of things, which is what happened in the case of Charles "Tookie" Williams. All the people in Holly Weird were crying foul because he was set to finally be executed decades after his crimes, but NO ONE there mentioned the horrific brutality in which he murdered his victims!
I pray for Justice for this man. I also pray for Mercy for him, may he be converted as Alessandro Serenelli was converted:
http://www.catholic-forum.com/saints/saintm09.htm