265 From the earliest centuries of the Church, some were clearly opposed to capital punishment. Lactantius, for example, held that “there ought to be no exception at all; that it is always unlawful to put a man to death”. Pope Nicholas I urged that efforts be made “to free from the punishment of death not only each of the innocent, but all the guilty as well”. During the trial of the murderers of two priests, Saint Augustine asked the judge not to take the life of the assassins with this argument: “We do not object to your depriving these wicked men of the freedom to commit further crimes. Our desire is rather that justice be satisfied without the taking of their lives or the maiming of their bodies in any part. And, at the same time, that by the coercive measures provided by the law, they be turned from their irrational fury to the calmness of men of sound mind, and from their evil deeds to some useful employment. This too is considered a condemnation, but who does not see that, when savage violence is restrained and remedies meant to produce repentance are provided, it should be considered a benefit rather than a mere punitive measure… Do not let the atrocity of their sins feed a desire for vengeance, but desire instead to heal the wounds which those deeds have inflicted on their souls”.
Source: Fratelli Tutti (Vatican.va)