Fr. John A. Hardon, S.J.
A prominent Roman Catholic theologian of the 20th century. 

... Equally important is the Pope's (Pius XII) insistence that capital punishment is morally defensible in every age and culture of Christianity. Why? Because the Church's teaching on "the coercive power of legitimate human authority" is based on "the sources of revelation and traditional doctrine." It is wrong, therefore "to say that these sources only contain ideas which are conditioned by historical circumstances." On the contrary, they have "a general and abiding validity." (Acta Apostolicae Sedis, 1955, pp 81-2).

http://www.therealpresence.org/archives/Sacred_Scripture/Sacred_Scripture_014.htm

It is remarkable what appeals to kindness and charity are made to repeal capital punishment. Two thousand years of the Church's defense of capital punishment are brushed aside.

http://www.catholicculture.org/culture/library/view.cfm?recnum=6871

Justice Antonin Scalia,  First Things Magazine, May 2002.

There have been Christian opponents of the death penalty, just as there have been Christian pacifists, but neither of those positions has ever been that of the Church. The current predominance of opposition to the death penalty is the legacy of Napoleon, Hegel, and Freud rather than St. Paul and St. Augustine.

 … Thomas More, who has long been regarded in this country as the patron saint of lawyers, and who has recently been declared by the Vatican the patron saint of politicians (I am not sure that is a promotion). One of the charges leveled by that canonized saint’s detractors was that, as Lord Chancellor, he was too quick to impose the death penalty.

… Is it prudent to imperil acceptance of the Church’s hard but traditional teachings on birth control and abortion and euthanasia (teachings that have been proclaimed in a binding manner, a distinction that the average Catholic layman is unlikely to grasp) by packaging them—under the wrapper “respect for life”—with another uncongenial doctrine that everyone knows does not represent the traditional Christian view? Perhaps, one is invited to conclude, all four of them are recently made–up. …

… Those ideologically driven to ferret out and proclaim a mistaken modern execution have not a single verifiable case to point to, whereas it is easy as pie to identify plainly guilty murderers who have been set free.

Justice Antonin Scalia is a devout Catholic. In 1986, Presiden Ronald Reagan appointed Scalia to the Supreme Court of the United States. As the longest-serving justice on the Court, Scalia is the senior associate justice and is the anchor of the Court's conservative wing. Scalia has repeatedly called upon his colleagues to strike down Roe v. Wade.

Judge Robert Bork’s - October, 2002, First Things Magazine

... My difficulty has to do with the Church adopting positions that may be taken to be binding on public affairs when it has no special, or sometimes even an adequate, understanding of the subject. If the Pope or the bishops express opinions on such matters, that is certainly their right. But they should be owed no particular deference, either by Catholics or others.

I argued a case for the government in which the defendant had told friends that he wanted sex with a young girl, went to a public swimming pool, seized a ten-year-old girl, threw her in the back of his pickup truck, drove her through town while she screamed futilely for help, took her to a river, raped her, drowned her, and then bought beer to drink while sharing his happy recollection with friends. If ever a man deserved the death sentence, he did, and he got it.

Life imprisonment does not, in any event, fully protect society. Imprisoned murderers have killed guards and other prisoners. They have been paroled or escaped and killed again. Just two years ago, seven hardened criminals, one of whom was serving eighteen life sentences, escaped from a maximum-security Texas prison. A few weeks later, while robbing a sporting goods store, they killed a police officer, shooting him thirteen times and then driving over his body. The blood of the murderers’ new victims is at least partially on the hands of those who make the execution of such killers impossible.

Robert Bork is an American legal scholar. In 1987, he was nominated to the Supreme Court by President Ronald Reagan but his nomination was rejected by the Senate under the leadership of Ted Kennedy and Joe Biden.On July 21, 2003 at age 76, Robert Bork was received into the Catholic Church. He has authored several books including, "Slouching Towards Gomorrah: Modern Liberalism and American Decline."

C. S. Lewis in Mere Christianity:

"Does loving your enemy mean not punishing him? No, for loving myself does not mean that I ought not to subject myself to punishment- even to death. If one had committed a murder, the right Christian thing to do would be to give yourself up to the police and be hanged. It is, therefore, in my opinion, perfectly right for a Christian judge to sentence a man to death or a Christian soldier to kill an enemy. It is no good quoting “Thou shall not kill.” There are two Greek words: the ordinary word to kill and the word to murder. And when Christ quotes that commandment He uses the word murder in all three accounts."

Charles W. Colson, Prison Fellowship :
"It is because humans are created in the image of God that capital punishment for premeditated murder was a perpetual obligation. The full range of biblical data weighs in its favor. This is the one crime in the Bible for which no restitution was possible (Numbers 35:31,33). ... The sanctity of human life is rooted in the universal creation ethic and thus retains its force in society. The Christian community is called upon to articulate standards of biblical justice, even when this may be unpopular. Capital justice is part of that non-negotiable standard. Society should execute capital offenders to balance the scales of moral judgement." 
From "Capital Punishment: A Personal Statement", by Charles W. Colson., a former opponent of capital punishment. He is spiritual advisor and friend to numerous death row inmates and the Founder of Prison Fellowship, the largest Christian ministry serving incarcerated prisoners.  

Pro life supporters who oppose capital punishment have strange judicial supporters.

All of the recent and current Supreme Court Justices who oppose capital punishment

are pro abortion.

All of the recent and current Supreme Court Justices who support capital punishment

are pro life.