I’m not sure that you can punish someone who has already had 71 years for freedom.
Sure, you could execute him, but you are not depriving him of anything but a few more days at the end of a life in a worn out body, and a mind not at the top.
This SOB needs to be punished. Not so much because a few days, weeks, months or a couple of years will make up for what he did (it won’t), but so that every other person who even thinks about doing something of like kind in the future will know that the rest of the world DOES care, and WILL hunt them down even when they are old bastards. It is much more about deterring the same thing from happening again, and less about actual punishment.