Catechism of the Catholic Church
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. 69
Infanticide, 70 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. 71
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.
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.