Today’s Catechism sections discuss capital punishment and intentional homicide. Supporting material comes from the Pastoral Constitution, “Gaudium et Spes”.

Capital Punishment

2266 The State's effort to contain the spread of behaviors injurious to human rights and the fundamental rules of civil coexistence corresponds to the requirement of watching over the common good. Legitimate public authority has the right and duty to inflict penalties commensurate with the gravity of the crime. The primary scope of the penalty is to redress the disorder caused by the offense. When his punishment is voluntarily accepted by the offender, it takes on the value of expiation. Moreover, punishment, in addition to preserving public order and the safety of persons, has a medicinal scope: as far as possible it should contribute to the correction of the offender.67

2267 The traditional teaching of the Church does not exclude, presupposing full ascertainment of the identity and responsibility of the offender, recourse to the death penalty, when this is the only practicable way to defend the lives of human beings effectively against the aggressor.
"If, instead, bloodless means are sufficient to defend against the aggressor and to protect the safety of persons, public authority should limit itself to such means, because they better correspond to the concrete conditions of the common good and are more in conformity to the dignity of the human person.
"Today, in fact, given the means at the State's disposal to effectively repress crime by rendering inoffensive the one who has committed it, without depriving him definitively of the possibility of redeeming himself, cases of absolute necessity for suppression of the offender 'today ... are very rare, if not practically non-existent.'[John Paul II, Evangelium vitae 56.]

Intentional homicide

2268 The fifth commandment forbids direct and intentional killing as gravely sinful. The murderer and those who cooperate voluntarily in murder commit a sin that cries out to heaven for vengeance.68

Infanticide,69 fratricide, parricide, and the murder of a spouse are especially grave crimes by reason of the natural bonds which they break. Concern for eugenics or public health cannot justify any murder, even if commanded by public authority.

2269 The fifth commandment forbids doing anything with the intention of indirectly bringing about a person's death. The moral law prohibits exposing someone to mortal danger without grave reason, as well as refusing assistance to a person in danger.

The acceptance by human society of murderous famines, without efforts to remedy them, is a scandalous injustice and a grave offense. Those whose usurious and avaricious dealings lead to the hunger and death of their brethren in the human family indirectly commit homicide, which is imputable to them.70

Unintentional killing is not morally imputable. But one is not exonerated from grave offense if, without proportionate reasons, he has acted in a way that brings about someone's death, even without the intention to do so.

The Pastoral Constitution, “Gaudium et Spes” (51) discusses the dignity of human life from conception.

For God, the Lord of life, has conferred on men the surpassing ministry of safeguarding life in a manner which is worthy of man. Therefore from the moment of its conception life must be guarded with the greatest care while abortion and infanticide are unspeakable crimes. The sexual characteristics of man and the human faculty of reproduction wonderfully exceed the dispositions of lower forms of life. Hence the acts themselves which are proper to conjugal love and which are exercised in accord with genuine human dignity must be honored with great reverence. Hence when there is question of harmonizing conjugal love with the responsible transmission of life, the moral aspects of any procedure does not depend solely on sincere intentions or on an evaluation of motives, but must be determined by objective standards. These, based on the nature of the human person and his acts, preserve the full sense of mutual self-giving and human procreation in the context of true love. Such a goal cannot be achieved unless the virtue of conjugal chastity is sincerely practiced. Relying on these principles, sons of the Church may not undertake methods of birth control which are found blameworthy by the teaching authority of the Church in its unfolding of the divine law.(14)

Footnotes

67 Cf. ? Lk 23:40-43.
68 Cf. ? Gen 4:10.
69 Cf. GS 51 # 3.
70 Cf. ? Am 8:4-10.