Adult prison for all of them, I think. If they are old enough to rob and shoot someone, they are old enough to get a cell with the big boys.
What I dont understand is all these people calling for the death sentence. Its amusing, ask anyone what they think of it and they will spend the day telling you why they think its wrong, but confront them with one story like this and strip away their ignorance, and they will fall just short of taking to the streets with forks and pickaxes.
(Im against the death sentence, by the by.)