Jana Riess discusses inaccuracies in "Under the Banner of Heaven" in its portrayal of Brigham Young's involvement in Joseph Smith's death.
Jane Clayson, "What 'Under the Banner of Heaven' gets right — and wrong — about Mormons," WBUR, May 4, 2022, accessed June 2, 2022
On whether the ‘Under the Banner of Heaven’ properly distinguishes between extremists and mainstream Mormons
“I think it is trying to do so and I think it does a better job at that than the book did. I would also say that with the dramatization, particularly of Brigham Young, that is told in these flashbacks into Mormon history, later on in the series around episode five, they're making this claim. It's a little bit subtle, but it seems to be there: that Brigham Young somehow engineered the death of Joseph Smith and that he was, "running the church in the months before Joseph's death." I had to rewind that and make sure that I was hearing it correctly, because that is so completely not true. Brigham Young wasn't even in Nauvoo, which is where the Mormons were living at the time. He was on a mission in the Eastern states that was part religious and part also as a campaign for Joseph Smith's run for president. So he wasn't even on the scene. And so for the show to make a claim that he is somehow engineering these events that culminate in the assassination of Joseph Smith is really problematic.”