Brigham Young says he would kill a cheating wife and her lover, so they could atone for their sins not covered by Christ's blood.
Brigham Young, "Instructions to the Bishops—Men Judged According to Their Knowledge—Organization of the Spirit and Body—Thought and Labor to Be Blended Together," Journal of Discourses, 26 vols. (Liverpool: Orson Pratt, 1856), 3:247
You say, "That man ought to die for transgressing the law of God." Let me suppose a case. Suppose you found your brother in bed with your wife, and put a javelin through both of them, you would be justified, and they would atone for their sins, and be received into the kingdom of God. I would at once do so in such a case; and under such circumstances I have no wife whom I love so well that I would not put a javelin through her heart, and I would do it with clean hands. [. . . ] There is not a man or woman, who violates the covenants made with their God, that will not be required to pay the debt. The blood of Christ will never wipe that out, your own blood must atone for it; and the judgments of the Almighty will come, sooner or later, and every man and woman will have to atone for breaking their covenants. To what degree? Will they have to go to hell? They are in hell enough now. I do not wish them a greater hell, when their consciences condemn them all the time.