The biblical and theological support for the death penalty far outweighs any alleged teachings to the contrary.
God/Jesus: 'Honor your father and your mother,' and 'Whoever curses father or mother must certainly be put to death.' Matthew 15:4. full context - Jesus used this reference to condemn the Pharisees for their intentional misinterpretation of God's Word, emphasizing that the Truth of God's Word must be enforced, which is precisely what He was doing with this well known passage. www.newadvent.org/bible/mat015.htm
Saint (& Pope) Pius V, "The just use of (executions), far from involving the crime of murder, is an act of paramount obedience to this (Fifth) Commandment which prohibits murder." "The Roman Catechism of the Council of Trent" (1566).
All interpretations, contrary to the biblical support of capital punishment, are false. Interpreters ought to listen to the Bible’s own agenda, rather than to squeeze from it implications for their own agenda. As the ancient rabbis taught, “Do not seek to be more righteous than your Creator.” (Ecclesiastes Rabbah 7.33.). Part of Synopsis of Professor Lloyd R. Bailey’s book Capital Punishment: What the Bible Says, Abingdon Press, 1987.
"Death Penalty Support: Christian and secular Scholars"
http://prodpinnc.blogspot.com/2009/07/death-penalty-support-modern-catholic.html
Christianity and the death penalty
http://www.prodeathpenalty.com/DP.html#F.Christianity
Catholic and other Christian References: Support for the Death Penalty,
http://homicidesurvivors.com/2006/10/12/catholic-and-other-christian-references-support-for-the-death-penalty.aspx
Quaker biblical scholar Dr. Gervas A. Carey: " . . . the decree of Genesis 9:5-6 is equally enduring and cannot be separated from the other pledges and instructions of its immediate context, Genesis 8:20-9:17; . . . that is true unless specific Biblical authority can be cited for the deletion, of which there appears to be none. It seems strange that any opponents of capital punishment who professes to recognize the authority of the Bible either overlook or disregard the divine decree in this covenant with Noah; . . . capital punishment should be recognized . . . as the divinely instituted penalty for murder; The basis of this decree . . . is as enduring as God; . . . murder not only deprives a man of a portion of his earthly life . . . it is a further sin against him as a creature made in the image of God and against God Himself whose image the murderer does not respect." (p. 111-113) Essays on the Death Penalty, T. Robert Ingram, ed., St. Thomas Press, Houston, 1963, 1992.
Pope Pius XII: "When it is a question of the execution of a man condemned to death it is then reserved to the public power to deprive the condemned of the benefit of life, in expiation of his fault, when already, by his fault, he has dispossessed himself of the right to live." 9/14/52
Jesus: "So Pilate said to (Jesus), "Do you not speak to me? Do you not know that I have power to release you and I have power to crucify you?" Jesus answered (him), "You would have no power over me if it had not been given to you from above." John 19:10-11
Jesus: Now one of the criminals hanging there reviled Jesus, saying, "Are you not the Messiah? Save yourself and us." The other, however, rebuking him, said in reply, "Have you no fear of God, for you are subject to the same condemnation? And indeed, we have been condemned justly, for the sentence we received corresponds to our crimes, but this man has done nothing criminal." Then he said, "Jesus, remember me when you come into your kingdom." (Jesus) replied to him, "Amen, I say to you, today you will be with me in Paradise." Luke 23: 39-43
Jesus: "You have heard the ancients were told, ˜YOU SHALL NOT COMMIT MURDER" and "Whoever commits murder shall be liable to the court". But I say to you that everyone who is angry with his brother shall be guilty before the court; and whoever shall say to his brother, "Raca", shall be guilty before the supreme court and whoever shall say, "You fool", shall be guilty enough to go into fiery hell." Matthew 5:17-22. Here, Jesus raises the bar. Not only are murderers subject to the death penalty, but those who have hatred in their hearts "shall be guilty enough to go into fiery hell" - an infinitely more severe sanction than any earthly death.
full context http://www.newadvent.org/bible/mat005.htm
The Holy Spirit: God, through the power and justice of the Holy Spirit, executed both Ananias and his wife, Saphira. Their crime? Lying to the Holy Spirit - to God - through Peter. Acts 5:1-11