Many Mormons seek solace in the thought that there were enough reliable witnesses to substantiate the Book of Mormon”‘s validity and justify their own faith in it. But just how reliable were these witnesses? Mormons often claim that none of them ever denied their testimony of the Book of Mormon. However, Brigham Young in the LDS Journal of Discourses says that “some of the witnesses of the Book of Mormon who handled the plates and conversed with the angels of God, were afterwards left to doubt and to disbelieve that they had ever seen an angel.” This must refer to Oliver Cowdrey, David Whitmer, and/or Martin Harris, who alone in their written testimonies (printed in the front of each copy of the Book of Mormon) claimed to have both handled the plates and seen an angel. The Journal of Discourses”‘ use of the plural (“some of the witnesses”) indicates at least two of them doubted, though one in this passage was identified as a member of the Quorum of the Twelve Apostles who fell away. 

For more information, see The Mormon Mirage 3rd Edition:  A Former Member Looks at the Mormon Church Today (Zondervan, 2009). Also available as an audiobook and as an expanded-text E-book for Nook, Kindle and other reading devices.