A Story of Violent Faith
The author of Into Thin Air here takes on the roots of a horrible murder in the Utah backwater, a murder undertaken by relatives of the deceased. He examines the founding of the Mormon faith, and how its unique properties lend themselves to the dangerous kinds of fundamentalist sects that lead followers towards violence. (This is primarily due to the decentralized nature of the faith and not any specific tenets, BTW.) But mostly, Krakauer delves into the history that the leadership of the LDS church would rather keep private - the unsavory occurrences of the Latter-Day-Saints' early years, and the notion that it was okay to lie, cheat, and steal from outsiders - non-Mormons.
Krakauer recounts the early history of the church, from its inception to the present day, in a tale interwoven with the lives of the murderers. The doctrine of personal revelation - the concept that God speaks individually to each person, if they wish to hear it - has led to splinter sects, those who believe that the mainstream church's renunciation of pologamy is wrong, and that it is each man's duty to wed multiple times, to many young women. (One such believer abducted a girl who would become nationally famous - Elizabeth Smart.) Further, many of these sects have their own doctrines and beliefs, separate from the main church, and any who do not follow those doctrines are shunned.
When one family turned toward polygamy, one wife had the courage to speak up, and assist her sisters-in-law who wished to escape the suddenly oppressive marriages. This angered two of the brothers, who later believed that it had been revealed to them that the woman should die, along with her infant daughter. Even now, decades later, the one who actually wielded the knife believes that God approves of his actions, and that he did the right thing.
Krakauer does not have any easy answers, though he suggests several reasons why the brothers may have believed as they did. However, this compelling narrative is not about reasons, but about a history of an American faith, a history few know.