Why pay to house, clothe and feed a mass murderer like that guy in Oslo last year?

In some cases there is no possibility of rehabilitation. Give the convicted multiple time or mass killers their due process and their appeal rights but if they are proven guilty upon appeal what good are they to society? They just take up prison space for life at taxpayer expense ...

One time manslaughter with no prior violent criminal convictions might be a case for a potential prison sentence.