Catechism of the Catholic Church §2261 — excerpt
Scripture specifies the prohibition contained in the fifth commandment: "Do not slay the innocent and the righteous." The deliberate murder of an innocent person is gravely contrary to the dignity of the human being, to the golden rule, and to the holiness of the Creator.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.