First, in Kennedy v. Louisiana (2008), the Supreme Court exceeded their authority and ruled that the death penalty is unconstitutional in all cases that do not involve murder or crimes against the State. The legislative option was closed out by an activist court exceeding their authority.
Second, I agree 100% that we have a moral responsibility to keep even the worst prisoners safe once we remove their ability to defend themselves. I have no objection to parents who kill these predators in the process of stopping the attack, but our government should not look the other way on what happens behind bars.
In this case what additional punishment can they give this individual?