The death penalty only fulfills special prevention by making sure 100% the individual doesn't commit crimes. General prevention is not achieved and retribution only sometimes. but even retribution is not supposed to be an eye for an eye. All sentences have a retribution part, you just got to balance it with the other two objectives/purposes of criminal law. A sentence merely based on retribution is not a mean to protect society, but merely a finality to accomplish revenge
Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you