I'm not sure what the latest Breivik thing is and looking it up might be inconvenient for what I'm about to say, so I'll just respond to the previous Breivik thing which was about his complaining about only having PS2 games or something:
I'm not sure mass murderers like him are motivated by the same things as other people. Something like what he did doesn't seem to fit into a normal hedonic calculus especially since a lot of killing spree perpetrators kill themselves (doesn't apply to him, but still). They seem to have a martyr/hero/Great Man of History complex, so being killed by the State might just be giving them what they want.
Given that, seems like to be an effective deterrent a punishment would have to be designed around the killers' unique motivations. So, making them live the most mediocre life possible, being trapped in a moderately unfashionable apartment and forced to suffer the indignity of playing slightly out-of-date video games all day, might actually be the perfect punishment.