Benjamin Winchester explains the origin of the Spaulding theory of Book of Mormon authorship.
Benjamin Winchester, The Origin of the Spaulding Story, Concerning the Manuscript Found (Philadelphia: Brown, Bicking & Guilpert, 1840), 3, 8-9
PREFACE
The following work is not Resigned as a vindication of the peculiar events of the church of Jesus Christ of Latter Day Saints-But simply an exposition of the means used, by the enemy of all righteousness, to stop the progress of inquiry, and prejudice the minds of those who know little or nothing of the religious faith of those who believe the Book of Mormon an inspired record of a fallen people; and thereby prevent examination and investigation. The writer has therefore esteemed it a duty devolving on him, to make a statement of facts coming under his own inspection; as well as those with which he has had ample opportunity of becoming cognizant.
...
During the six or eight months that Mr. H. was preaching in the State of Pennsylvania, (part of the time he belonged to the church, and part of it he was lecturing against it;) he formed a large circle of acquaintance, and mingled with all sorts and classes of people. While in a small village, called the Jackson settlement, (a place that is famous for infidels,) he became familiar with a family of the name of Jackson, and others, who were personally acquainted with the now celebrated Solomon Spaulding, who is reputed to be the legitimate author of the Book of Mormon. Here, while in conversation with them, Mr. H. learned that Mr. S., while alive, wrote a work called the Manuscript Found. Not that any of these persons had the most distant idea that this novel had ever been converted into the Book of Mormon; or that there was any connexion between them. Indeed, Mr. Jackson, who had read both the Book of Mormon, and Spaulding's manuscript, told Mr. H. when he came to get his signature to a writing, testifying to the probability that Mr. S.'s manuscript had been converted into the Book of Mormon; that there was no agreement between them; for, said he, Mr. S.'s manuscript was a very small work, in the form of a novel, saying not one word about the children of Israel, but professed to give an account of a race of people who originated from the Romans, which Mr. S. said he had translated from a Latin parchment that he had found. The Book of Mormon, he added, purports to be written by a branch of the house of Israel; is written in a different style, and altogether different; for this reason Mr. Jackson refused to lend his name to the lie, and expressed his indignation and contempt at the base and wicked project to deceive the public.
Mr. Jackson was a disinterested man, and a good citizen.
Mr. H., after learning that such a novel had been written, In order to carry out his designs, resolved to make the fact, that a novel had been written, the foundation of a notorious fabrication; and at the same time make it appear as plausible as possible, to deceive the world, and induce them to account for the origin of the Book of Mormon in some other way than the truth.
After Mr. H. had learned what I have before mentioned, he immediately repaired to Kirtland, Ohio, and made an appointment to deliver a lecture, on what he called AntiMormonism; and made a special request that all who were opposed to the church of Latter Day Saints should attend, which they did, both priest and people, and composed a council, which I suppose resembled strongly the conclave of Hell, or the Jewish Sanhedrin, when they met to put down Jesus and his doctrine.
Here Mr. H. had ample opportunity to display his talent for talking, to a people who listened with breathless attention, and were greedy in devouring his words, expecting to hear some great secret divulged. Mr. H. told them that he had been travelling in the State of Pennsylvania, lecturing against Mormonism; and that he had learned that one Mr. Spaulding had written a romance, and the probability was, that it had, by some means, fallen into the hands of Sidney Rigdon and that he had converted it into the Book of Mormon. Mr. H. stated also, that he intended to write a book, called Mormonism Unveiled, which he said would divulge the whole secret.