1845. Unlawful killing of the innocent is a most heinous crime.
(a) It is an injury to the rights of God over human life, and is forbidden in the Fifth Commandment of the Decalogue: “Thou shalt not kill” (Exod., xx. 13). To judges the special command was given: “The innocent and just person thou shalt not put to death” (Exod., xxiii. 7). The man-slayer destroys the image of God, a crime so detestable that in Scripture God declares that He will revenge the blood of man, even though shed by a beast (Gen., ix. 5; Exod., xxi. 28).
(b) It is a most grave sin against the individual, for it deprives him of his chief natural good and the means of securing and enjoying many great spiritual goods. If the person killed desired or asked for death, no injustice is done to him, since he waived his right, but uncharitableness is committed, since the neighbor’s life should be loved, and the uncharitableness is greater according as the person is more worthy of love. Scripture numbers murder among the sins that cry to heaven for vengeance (Gen., iv. 10, ix. 5).
(c) It is an outrage against society, for such killing unduly deprives the community of one of its members, causes scandal and disturbs the peace. Hence, the law has always inflicted the severest punishment on slayers of the innocent.
1846. Since the end does not justify the means, the following ends do not justify the direct and intentional killing of innocent persons:
(a) the public good does not excuse, for example, if an enemy were to threaten destruction against a city unless it put to death an innocent person who dwelt in its borders. The criminal on account of his lawlessness is an obstacle to the common good, but the law-abiding citizen promotes the common good and it would be harmful to the public peace if he could be put to death without any fault of his own. The State is for the citizen, not the citizen for the State. But if the common safety depended on the sacrifice of one man’s life, charity and patriotism would require this man to make the sacrifice spontaneously (see 1169); that is, he should deliver himself to the enemy, and were he to refuse, it seems the community would have the right to deliver him. Similarly, it is not lawful to kill hostages, even though the enemy has broken faith, or killed one’s subjects;
(b) the private good of other individuals does not excuse; for example, it is not lawful to kill a maniac lest he do harm to those around him, at least unless the conditions of unjust aggression are fulfilled. Similarly, it is not lawful to kill a woman with child, in order to baptize the child;
(c) the private good of the individual himself does not excuse; for example, it is not lawful to shoot or poison those who are mortally wounded or suffering from an incurable disease, or who are old and helpless, in order to spare them suffering. But one may give a person at the point of death a medicine that may hasten the end, if there is good hope that it will cure him and other remedies are futile, for the purpose is not to kill but to cure (see 2485). It is lawful also for embalmers to puncture the heart or sever an artery of a person who seems to be dead, if there are certain signs of his death, for the purpose is not to kill this person, but to free his friends from fear that he is buried alive.
1847. Indirect or Unintentional Killing of the Innocent.—Indirect and unintentional killing of the innocent is lawful (1872) only when there is a reason of sufficient gravity (i.e., one of a value proportionate to the life of the innocent person).
(a) The public safety is such a sufficient reason. Thus, in time of war it is lawful to attack a city, even though the death of many non-combatants will result, or to charge the enemy, even though innocent persons have been placed by the latter as a shield to his front ranks.