WBS says that blood atonement was introduced in Nauvoo after the martyrdom.

Apr 1892
Speech / Court Transcript
William B. Smith

William B. Smith, affidavit in Abstract of Evidence: Temple Lot Case (Lamoni, IA: Herald Publishing House and Bindery, 1893), 93-4

Herald Publishing House
William B. Smith
Circuit Court of the United States, Western District of Missouri, Western Division, at Kansas City

There were three or four propositions or doctrines that were introduced into the church after the death of my brother in June, 1844, under the council of a part of the Twelve. One point was—and it had never been taught previous to that time—that Adam was God, and also that Moses was a man-god. Another doctrine was that of "blood atonement," meaning that if a man disobeyed the propositions of that council, meaning the remaining Twelve, he had to pay for it by the forfeiture of his life and atone for the sin by the shedding of his own blood, or allowing it to be shed by others. That was blood atonement for you, and it had never been taught in the old church. So they brought the matter down to the Adam-God doctrine, and the Moses-God doctrine, and finally these men that were left or composed the Twelve at that time brought in Joseph Smith as another god, one of their gods under the Adam-God doctrine and the blood-atonement doctrine.

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