FJC and GLK explain the doctrine of blood atonement.
Frank J. Cannon and George L. Knapp, Brigham Young and His Mormon Empire (New York: Fleming H. Revell Company, 1913), 264-265
Weaving in and out of these hair-raising threats we get a glimpse of a doctrine soon to be published to the world as "blood atonement." This doctrine was based on the words of Paul—Hebrews ix, 22—"Without the shedding of blood there is no remission." Stripped of ecclesiastical verbiage, the doctrine of blood atonement was that some sins could be expiated only by spilling the blood of the sinner; and that in such cases, it was the duty of all true believers to cut a man's throat for the saving of his soul.