searcher of mind and heart,
Let me witness the vengeance you take on them,
for to you I have entrusted my cause!
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.
Infanticide, 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.
-- CCC 2268