Lorenzo Saunders to Thomas Gregg (January 28, 1885):
“Smith and Rigdon had an intimacy but it was very secret and still and there was a mediator between them and that was Cowdery. The [Spalding] manuscript was stolen by Rigdon and modelled over by him and then handed over to Cowdery and he copied them and Smith sat behind the curtain and handed them out to Cowdery and as fast as Cowdery copied them, they was handed over to Martin Harris and he took them to Egbert Granden [sic], the one who printed them, and Gilbert set the type.”
Pages 132-133 in True Origin of the Book of Mormon (1914) by Charles Shook.
Also cited on page 129 in H. A. David et al. (1997), “Who Really Wrote The Book of Mormon?”