Whether we choose to execute or not, innocent people may die. While it is often asserted that innocent people have been executed, this is only a presumption. It has not been shown to be true (in the US at least since it was allowed in 1973). Even if we assume it is true, however, it is surely true that prisoners who have been incarcerated for one murder and not executed have gone on to commit others, both in and out of prisons. There is no completely safe choice here; innocents are at risk either way.
There is no way this can be known, and it seems unlikely in the extreme. All punishments deter some and it is not credible to believe that only the severest penalty of all deters no one.*Homicide is rare among slaves because of their dread and fear of capital punishment, whereas among the rich it is constantly committed because of their confident hope of immunity. *
(Salvian, On the Government of God, Bk IV, ch 5)
The catechism itself cites an example of capital punishment being the source of just such a reformation.(CCC 2266) Moreover, punishment, in addition to preserving public order and the safety of persons, has a medicinal scope: as far as possible it should contribute to the correction of the offender.(67)
*(67) Lk 23: 40-43 - ref the salvation of the good thief *
Life is surely sacred, which is why God taught that the person who unjustly takes the life of another forfeits his own.(CCC 2260) *For your lifeblood I will surely require a reckoning… Whoever sheds the blood of man, by man shall his blood be shed; for God made man in his own image. *(Gn 5:6)
Ender