Let us take him seriously. The basis of capital punishment is equity. In business, we would call it the just price. Having taken a victim's life, we search for a proper payment for this crime. The Bible makes it clear that the execution of murderers is the duty of the civil authority.
Biblical revisionists try to argue that the Bible opposes capital punishment.
Christ may have showed Sovereign mercy to the woman caught in adultery, who was guilty of a capital offense according to Mosaic law, but none of his disciples took this solitary act of Divine forgiveness to be an abrogation of the punishing power of the civil government. The Judeo-Christian tradition does not disparage the utilitarian aspect of executing murderers. The principle of punishment, like the rod of correction, acts through fear and reason to restrain evil. Capital punishment, therefore, is an unarguable deterrent for murder, violence, and crime. Second, we know that any murderer who is executed will not murder again.