Under the Banner of Heaven - Jon Krakauer

In 1984, God ordered Ron and Dan Lafferty to "remove" (i.e. kill) their young sister-in-law and her baby. Both men were Mormon Fundamentalists who took faith and religion to the extreme. This book describes the murders and also gives a current status and history of the religion all the way back to LDS founder Joseph Smith. Although primarily critical of Fundamentalists, it doesn't show the mainstream LDS Church in a favorable light either.