Ellen E. Dickinson claims that Sidney Rigdon did not steal the Spaulding manuscript, but he did copy it.
Ellen E. Dickinson, New Light on Mormonism (New York: Funk & Wagnalls, 1885), 23-24
Soon after Mrs. Davison went to Munson the whole country was filled with an agitation in regard to a new religious faith called Mormonism; and the report that it was founded on Solomon Spaulding’s romance, "Manuscript Found,” quickly followed, to the immense surprise of Mrs. Davison, Mrs. McKinstry, and every one connected with the author of that remarkable and unfortunate novel. Then a report was directly carried to these ladies, that a great meeting of Mormons had been held at Conneaut, Ohio, and that on one occasion, when the "Book of Mormon” was read before the assemblage, John Spaulding and Mr. Lake, the former partners of Solomon Spaulding, and many other persons who were present, recognized its similarity to the story called "The Manuscript Found," with which they had been so familiar years before (see statements 4th and 5th, Appendix) in that very locality.
She was not a little excited over what. she heard of the Mormons, and Mrs. McKinstry says she remembers how her mother talked on the subject, expressing a firm conviction that Sidney Rigdon had copied the manuscript, which had been in Mr. Patterson’s office in Pittsburg. She also said at this time that Mr. Spaulding had assured her that he recovered his original manuscript when Mr. Patterson refused to publish it; and she never wavered or doubted in this belief.