"...  a serious commitment to the sanctity of human life may well compel, rather than forbid, that form of punishment."

" ... if those findings are right, capital punishment has a strong claim to being not merely morally permissible, but morally obligatory—above all from the standpoint of those who wish to protect life."

This highly acclaimed 2005 study is from AEI-Brookings. If you download the study, the first page is blank, so scroll down. - www.aei.org

This 44 pages study is by two Harvard law professors, Cass R. Sunstein and Adrian Vermeule,

who were formerly opposed to capital punishment. Below are excerpts from their Summary and Conclusion. (emphasis added)

Executive Summary

Recent evidence suggests that capital punishment may have a significant deterrent effect, preventing as many as eighteen or more murders for each execution. This evidence greatly unsettles moral objections to the death penalty, because it suggests that a refusal to impose that penalty condemns numerous innocent people to death. Capital punishment thus presents a life-life tradeoff, and a serious commitment to the sanctity of human life may well compel, rather than forbid, that form of punishment.

Moral objections to the death penalty frequently depend on a distinction between acts and omissions, but that distinction is misleading in this context, because government is a special kind of moral agent. The familiar problems with capital punishment - potential error, irreversibility, arbitrariness, and racial skew - do not argue in favor of abolition, because the world of homicide suffers from those same problems in even more acute form. The widespread failure to appreciate the life-life tradeoffs involved in capital punishment may depend on cognitive processes that fail to treat "statistical lives" with the seriousness that they deserve.

Conclusion

Any objection to capital punishment, we believe, must rely on something other than abstract injunctions against the taking of life. If the recent evidence of deterrence is ultimately shown to be correct, then opponents of capital punishment will face an uphill struggle on moral grounds. If each execution saves many innocent lives, the harms of capital punishment would have to be very great to justify its abolition, far greater than most critics have heretofore alleged. There is always residual uncertainty in social science and legal policy, and in this domain the empirical controversy continues; we have attempted to describe, rather than to defend, the recent findings. But if those findings are right, capital punishment has a strong claim to being not merely morally permissible, but morally obligatory—above all from the standpoint of those who wish to protect life.

Death penalty opponents will disparage any study which shows that capital punishment saves innocent lives. They ignore scripture and the traditional teaching of the Catholic faith and substitute their own personal feelings and opinion. But do we really need studies to point out the obvious. Take two Identical worlds, one only with capital punishment, in which would the most innocents be murdered?