None of the witnesses ever denied their testimony of the Book of Mormon. This is a remarkable fact seeing that many of them left the church and were even hostile to Joseph Smith.
As an example, Oliver Cowdery said before being re-baptized:
I wrote, with my own pen, the entire Book of Mormon (save a few pages) as it fell from the lips of the Prophet Joseph, as he translated it by the gift and power of God, by the means of the Urim and Thummim, or as it is called by the book, Holy Interpreters. I beheld with my eyes, and handled with my hands, the gold plates from which it was transcribed. I also saw with my eyes and handled with my hands the Holy Interpreters. That book is true. …It contains the everlasting gospel, and came forth to the children of men in fulfillment of the revelations of John, where he says he saw an angel come with the everlasting gospel to preach to every nation, kindred, tongue and people. It contains principles of salvation; and if you, my hearers, will walk by its light and obey its precepts, you will be saved with an everlasting salvation in the kingdom of God on high.– Andrew Jenson, LDS Biographical Encyclopedia (Salt Lake City: Andrew Jenson History Company, 1901), 1:246
If the Book of Mormon was a fraud then surely one of the witnesses would have let slip the truth or confessed it at some point? Don’t the life-long testimonies of all these people strongly contradict all alternative theories of the Book of Mormon?