At the heart of Catholic teaching on the death penalty is the belief that " Human life is sacred because from its beginning it involves the creative action of God and it remains for ever in a special relationship with the Creator, who is its sole end…” (Catechism, No. 2258).
Regarding the death penalty, the catechism of the Catholic Church states:
“Assuming that the guilty party's identity and responsibility have been fully determined, the traditional teaching of the Church does not exclude recourse to the death penalty, if this is the only possible way of effectively defending human lives against the unjust aggressor.
If, however, non-lethal means are sufficient to defend and protect people's safety from the aggressor, authority will limit itself to such means, as these are more in keeping with the concrete conditions of the common good and more in conformity with the dignity of the human person.
Today, in fact, as a consequence of the possibilities which the state has for effectively preventing crime, by rendering one who has committed an offense incapable of doing harm—without definitively taking away from him the possibility of redeeming himself—the cases in which the execution of the offender is an absolute necessity "are very rare, if not practically non-existent”(#2267).
Pope Francis on the Death Penalty
“It is impossible to imagine that states today cannot make use of another means than capital punishment to defend peoples’ lives from an unjust aggressor … All Christians and people of good will are thus called today to struggle not only for abolition of the death penalty, whether it be legal or illegal and in all its forms, but also to improve prison conditions, out of respect for the human dignity of persons deprived of their liberty.” International Association of Criminal Law Address 10/24/2014
"Nowadays the death penalty is inadmissible, no matter how serious the crime committed. It is an offence against the inviolability of life and the dignity of the human person, which contradicts God’s plan for man and society, and his merciful justice, and impedes the penalty from fulfilling any just objective. It does not render justice to the victims, but rather fosters vengeance…”
“The death penalty is contrary to the sentiment of humanitas and to divine mercy, which must be the model for human justice. … There is discussion in some quarters about the method of killing, as if it were possible to find ways of 'getting it right'. … But there is no humane way of killing another person…”
“Dear friends, I encourage you to continue with your work, as the world needs witnesses of God's mercy and tenderness, and may the Lord Jesus grant the gift of wisdom, so that the action taken against this cruel punishment may be successful and fruitful". International Commission Against the Death Penalty Address 3/20/2015
Death Penalty Resources
Catholic Bishops of Ohio Teaching Statements on the Death Penalty