SALT LAKE CITY (AP) Best-selling author Jon Krakauer has built a reputation on gripping portrayals of those who push their physical limits. Now the writer has set his sights on spiritual extremes, and his upcoming book is already creating headaches for the image-conscious Mormon church.
''Under the Banner of Heaven: A Story of Violent Faith,'' which reaches bookstores Tuesday, looks at the dangers of religious extremism through those who claim to follow the original teachings of the Mormon church, a tenet of which was polygamy.
These Mormon breakaways, who often call themselves fundamentalists, still practice polygamy even though The Church of Jesus Christ of Latter-day Saints officially abandoned the practice in 1890 and works to this day to distance itself from the subject.
Krakauer, who declined to be interviewed, is best known for ''Into Thin Air,'' his firsthand account of a doomed expedition on Mount Everest. That book, along with his earlier ''Into the Wild,'' were national best sellers.
In ''Under the Banner of Heaven,'' Krakauer turns his attention to the 1984 murders of Brenda Lafferty and her 15-month-old daughter, Erica, in rural Utah at the hands of Brenda's fundamentalist brothers-in-law.
The author uses those deaths as the basis for an argument that, because of Mormon inconsistencies and silences about the dark corners of the faith's past, the LDS church has been unable to break free from embarrassing and sometimes tragic episodes.
The church, meanwhile, has been forceful in rebuking Krakauer's book. Spokesman Michael Otterson called the writer's attempt to link religious zealots with Mormon history and doctrine ''a full-frontal assault on the veracity of the modern church.''
The slayings that form the basic story line were committed by Dan and Ron Lafferty, who slit their victims' throats with a 10-inch boning knife and later claimed God had ordered the slayings. The men were tried separately; Dan Lafferty is serving a life sentence, and Ron Lafferty who claimed to have the revelation to kill is on death row.
With Dan Lafferty as a main source, Krakauer writes that the brothers decided to practice polygamy and committed the killings because Brenda opposed them.
Weaving details of the deaths throughout the book, ''Under the Banner of Heaven'' tries to add a larger context to the killings and their alleged connection to Mormon fundamentalism.
It examines the secretive communities of polygamists, those who have given up the practice, and the Elizabeth Smart kidnapping case. The girl's alleged abductor, Brian David Mitchell, claims God told him to take Elizabeth as a ''sister wife.''
The book also devotes long sections to Mormon founder Joseph Smith and his revelation that believers in the faith should practice polygamy.
Though Smith is regarded by the Latter-day Saints as a prophet directly and uniquely guided by God, Krakauer characterizes him as a grifter and philanderer. He also explores the violent chapters of history, including the religion's role in the massacre of California-bound pioneers in 1857.
Krakauer's ''basic thesis appears to be that people who are religious are irrational, and that irrational people do strange things,'' Otterson said. ''He does a huge disservice to his readers by promulgating old stereotypes.''
The Mormon church has nothing to do with fundamentalists, church officials say. It excommunicates those who advocate plural marriage. Still, zealots such as Lafferty and Mitchell tarnish the church's image, and polygamy remains inextricably linked to the church's early decades.
In 1843, Smith disclosed his revelation that polygamy, restored by prophecy from the patriarchal Old Testament, was an essential ingredient of eternal exaltation.
Smith's teachings on polygamy remain in the church's four volumes of scripture, which has been used as a justification for Mitchell and thousands of others to defy Mormonism and establish sects where men take multiple wives, some as young as 12.
Krakauer notes that even after the church banned the practice as a condition of Utah's statehood, some Mormon leaders still took multiple wives after 1890.
Publishing house Doubleday has printed 350,000 copies of ''Under the Banner of Heaven'' so far, and early buzz has been favorable to the book. The Wall Street Journal and USA Today have recommended it in summer reading lists, and GQ magazine has featured excerpts.
But the LDS church-owned Deseret Book chain has already said it won't stock Krakauer's latest. ''We believe, after reviewing the book, that it will alienate and offend a majority of our customers,'' said spokeswoman Gail Brown.
Krakauer's language in the book is pointed: ''Mormon authorities treat the fundamentalists as they would a crazy uncle they try to keep the 'polygs' hidden in the attic, safely out of sight, but the fundamentalists always seem to be sneaking out to appear in public at inopportune moments to create unsavory scenes, embarrassing the entire LDS clan.''
Church historian Richard Turley said Krakauer has taken a sensational approach to the faith's history.
''Ostensibly focused on murders committed by brothers who had been excommunicated from the church, Krakauer's book is actually a condemnation of religion generally,'' Turley wrote in a review.
Krakauer shot back in an equally blunt written statement, accusing the church of continuing to distort its past.
''I am especially disappointed,'' he wrote, ''that they feel such an urgent need to attack writers, like me, who present balanced, carefully researched accounts of Mormon history that happen to diverge from the official, highly expurgated church version.''
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