http://rsc.byu.edu/archived/selected-articles/who-really-wrote-gospels-study-traditional-authorship

[We have] some historical evidence of Joseph Smith’s participation in their preparation, and acknowledge two recent authorship studies which conclude that others, particularly Sidney Rigdon, were also involved…

Both studies conclude that Sidney Rigdon was heavily involved, and that Joseph Smith was probably the author of Lecture 2. The differences [in wordprint studies] suggest that Joseph Smith had less to do with Lectures 3, 4, and 6…and that William W. Phelps and/or Parley P. Pratt could have had at least some editorial influence on Lecture 5…What then can we conclude about authorship of the Lectures on Faith?

It is clear that several of the brethren participated in writing them.

It is also clear that Joseph Smith and perhaps others prepared them for publication after they were written…