Does Bill O'Reilly use a ghostwriter for his books?

Bill O'Reilly has written several of his historical books in partnership with historian Martin Dugard, including "Killing Jesus," "Killing Kennedy" and "Killing Lincoln." He takes sole credit for all of his other books.

Martin Dugard is credited in the books that he worked with O'Reilly on, though it is not always clear who did most of the writing.

O'Reilly claims sole authorship of his other books, but critics have pointed out it seems very unlikely he would have time to research and write these books at the pace he does while also working as a television host. As of March 2015, there is no hard evidence of any ghostwriting.