I don’t know about others, but I don’t think anybody deserves to die necessarily. It is faaaaar too merciful a fate for horrible people. I believe the worst of humanity - rapists, murderers, child abusers, etc. - deserve to live long, painful, oh so horrible lives.
My choice would be to put them inside of a 3 meter cube of steel, welded shut, with only a hamster bottle for water, a hole in the bottom for waste, and a nutrient paste dispensing chute. When the prisoner eventually dies, it is bury the whole thing out in the desert to be their unmarked tomb.