What should retributive punishment look like in a just society?

From my (admittedly limited) understanding of Catholic teaching, the death penalty is never a morally justified punishment in today's American legal system.  There should accordingly be much rejoicing over New Mexico's repeal of the death penalty this week.  As Bishop Ramirez of Las Cruces said, Governor Richardson "has made New Mexico a leader in turning away from the death penalty with all its moral problems and issues of fairness and justice."  One of the governor's explanations struck me, though, as standing in some tension with the overarching commitment to human dignity that the death penalty's repeal represents.  After visiting the maximum-security cells where life-without-parole inmates would be housed, he explained, "my conclusion was those cells are something that may be worse than death."

I realize that the governor's statement probably had a lot to do with politics.  But it raises a deeper set of questions.  I do not dispute that a just society can incorporate a retributive element into its criminal punishments.  But does retribution, properly understood, mean that we should seek to house inmates in a way that "may be worse than death?"  Does retribution mean that we should inflict a certain degree of suffering on criminals?  Does retribution still need to be carried out consistently with living conditions that are recognizably human and support a certain level of physical, mental, and spiritual well-being for the inmate?  If so, is it fair to characterize a Catholic view of retribution in criminal punishment as limiting retribution to a deprivation of liberty while forbidding any deliberate infliction of suffering that is independent from the deprivation of liberty itself?