I can't remember where or when I heard about this book (I think it's in several books), but I heard good things about it, and I wanted to read it for myself. Under the Banner of Heaven is supposed to be the Lafferty murders, but it's actually a look at mormon fundamentalism and the history of mormonism.
The Lafferty murders refer to the deaths of Brenda and Erica Lafferty, mother and daughter pair. The murderers were Brenda's brother-in-laws, Ron and Dan, who admit to killing, but not to being guilty. Why? Because they believe the murders were divinely ordained. This idea stems from one section of mormon doctrine known as "blood atonement", or as the book says "certain grievous acts committed against Mormons, as Brigham explained it, could be rectified only if the "sinners have their blood spilt upon the ground." ". And what was the grievous sin of Brenda and Erica? Brenda stood up for herself and refused to adopt the policies of fundamental mormonism, which include polygamy. She also stood up for her abused sister-in-law (Ron's ex-wife), encouraging her to divorce her abusive husband, and very dangerously for her, she was smart and could beat the brothers in their own arguments for fundamentalism. Erica's sin was that Brenda was her mom.
What I consider the most disturbing part of the case is that it could have been prevented. Brenda's husband knew about his brother's plans, but kept mum. Others of their circle knew, and one even wrote an affidavit, but no one stepped in. Essentially, Brenda and Erica were like sheep to slaughter, because they were kept in the dark.
Along with an analysis of this case, the author goes into great detail about mormon history, from its roots and how it diverged from Christianity, to the establishment of the current Salt Lake city, and how the fundamentalist mormons appeared. At first, I didn't understand why the author was going into such great detail, but after reading the book, I think I understand. If you don't know anything about the background of Ron and Dan Lafferty, there is no hope of understanding why they did what they did. It's not about justifying their actions or finding sympathy for them, it's about illuminating their reasons.
All in all, this was an absorbing and horrifying book. I've no doubt most mormons are peaceful people (even if I strong disagree with their theology), but fundamentalist mormonism scares me to the core.