Death by lethal injection is efficient but I would have to say that death by one thousand stab wounds is much more satisfying. Wait for him to see the white light then, give him a blood transfusion to bring him back to coherence and then set him on fire. Put the fire out and then dump him in a salty ocean of your choice with a 100 pound weight suit. Resuscitate, and then make him watch the series finale of How I Met Your Mother on repeat for eternity, locked in in a room with nothing but a sweaty underwear noose from Super Bowl XX.
That is still not enough to rectify his actions.
Judy Clarke having represented so many killers, I wonder how she can even sleep at night! Fighting for her clients to live the remainder of their lives in prison.. What's her cut of the deal?