The victim doesn't even HAVE their life any more. The only proportional punishment for that is removing the killers freedom for the rest of THEIR lives. I can't really suggest blanket execution for murderers, I'm kinda ambivalent towards the death sentence. Not convinced the state should have the legal right to kill citizens, even murderers. It's a case by case basis for me.
It's clearly not deterring anyone in that stupid country. Rehabilitation is the best way IMO. There is a reason people kill. Lets find out why, and fix them. Why take two lives, when we can just take one?