Complete title: The Catechism of St. Thomas Aquinas
THE EIGHTH COMMANDMENT: "Thou Shalt Not Bear False Witness Against Thy Neighbor."
The references used to back this up are to other parts of the Bible. I have always wondered about the fact that there is not a commandment that directly prohibits lying. Of course there are a few occasions when lying may appear to be the lesser of two evils. But surely the decision of when these times occur is a slippery slope.
Here's one that happened to me recently that doesn't even involve life or death: I was asked a direct question by someone, which, had I answered it truthfully, would have ruined a surprise party that I knew was being planned for her. The party turned out to be a complete success. (Except for the lying part.)
Another one that often comes up on this website is whether it is OK to lie about one's political opponent. This is usually justified on the basis that the opponent represents the essence of evil, so lying and spreading poorly-justified rumors about them is fair game.
Of course one source of impetus for the spreading of possibly false rumors is that other people don't sufficiently appreciate the "evilness" in your opponent so the evilness needs to be boosted a little.
On the other hand someone who does have a strong sense of the evil in another person will tend to believe all the rumors about them.
Of course if someone really is evil, then it will only be necessary to tell the exact truth about them to describe their evilness.