You could put them in solitary for a spell if they play up, or take away privileges for 6 months like tv, computer games etc. We're talking about sane people here who are simply malignant. Otherwise they would have been found to be insane or with diminished responsibility
I do think a prisoner should be present to hear the ruling by the judge. And relatives of a deceased should have the small satisfaction of witnessing that.
I don't think there should be the death penalty across the board for all murders.
But, when a **** has admitted to mass murder and said they did it "because they're evil", no more time and expense should be wasted on them imo.