Was God’s ancient commandment “You shall not kill” (Ex 20:13) understood as an absolute statement, forbidding any taking of human life?  Apparently not, since the same divine law called for the death penalty (see Lv 20:2-21, 27).

For this reason, the Catholic Church reads the commandment against killing in the light of other biblical passages that specify its meaning: “The innocent and the just you shall not put to death, nor shall you acquit the guilty” (Ex 23:7).  The commandment thus forbids the taking of innocent life; execution of criminals may be another matter.

Of course, Christians are not obliged to practice all of the Old Testament laws (see Gal 3:23-25).  Nor, when the contemporary state punishes crimes censured in the Old Testament, must we demand that it impose as severe a penalty as God required of the ancient Israelites (see Jn 7:53-8:11).  Nevertheless, the Church has traditionally allowed for the possibility of capital punishment for extremely serious crimes.

Why?  Because societies may legitimately defend themselves — just as individuals may — and the defense of the common good depends upon rendering an unjust aggressor incapable of harming others.  In fact, such a defense may be not only a right but even a grave duty for public officials who are responsible to protect the lives of others (see Rom 13:3-4).

Must the aggressor be put to death to be rendered incapable of harm?  The Catechism explains:

Assuming that the guilty part’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, … the cases in which the execution of the offender is an absolute necessity “are very rare, if not practically non-existent” (Blessed Pope John Paul II, Evangelium vitae 56).  [2267, emphasis added]

Related Scripture:

Texts Cited: Ex 20:13; 23:7  •  Lv 20:2-21, 27  •  Jn 7:53-8:11  •  Rom 13:3-4  •  Gal 3:23-25
General: Gn 9:5-6  •  Dt 32:35  •  Mt 5:21-24; 38-40; 43-48  •  Rom 12:19  •  Heb 10:30
Catechism of the Catholic Church: 2261-2268  •  2320-2321