How man, in the image of God, meets appropriate justice in the abhorrent case of murder

I gathered this interpretation from the wise John Piper:

The covenant with Noah in Genesis chapter 9: Whoever sheds mans blood, by man his blood should be shed. For in the image of God he made man. The principle of capital punishment is the only fitting response to anybody who murders a human being. Human beings are so incredibly unique and significant that when there is a high handed crime to take another human beings life, the only way to settle accounts and uphold the dignity of life is to take that persons life. The image of God is the key in this covenant. The principle of capital punishment is biblical and right. What about Mercy? To want mercy is good. But that mercy would take form in a social setting where you don’t release criminals on the world. It would take the form of wanting him to be forgiven, praying for him, perhaps even visiting him in prison and offering to forgive him. But that forgiveness does not say, “I think it would be a good idea if he got let go or let up,” if he got a miscarriage of justice in the form of a lesser sentence of life in prison or pardoned. He will be let go in heaven, but here society won’t work. Romans 13 sets it up so that the government carries the sword to reward the good and to punish the evil, because society won’t work if governments don’t carry swords, prisons, fines, death penalties. So yes, it’s right to want mercy for criminals—to forgive them, not to hold grudges against them—and to want them to be punished.