I think he should be forced to suffer "Old Sparky" that sometimes malfunctions, necessitating several painful attempts. I would like to see the shooting flames out his eye sockets. It may not be the most humane method, but his crime wasn't exactly humane either. It is certainly proper justice.
I'm reminded of that unpleasant "dry sponge" scene in The Green Mile.
I don't think it's necessary for us, as observers, to become sadistic and vengeful over it. I'm content to let Scott's Creator deal out the punishment. If he gets the death penalty, that justice will begin more quickly though.