... So the diary [William Law diary] covers the period when William Law was becoming disillusioned with the Prophet. It shows him to have been very upset with the Prophet. At the end in commenting about the death of the Prophet, William Law calls him a charlatan, a false prophet, not a good person. William Law says he first became upset with the Prophet because his wife, Jane, who was pregnant, was asked by the Prophet to be his wife. William Law did not believe in polygamy, was revolted by the idea and by the way in which the Prophet approached his, William's, wife to be his, Joseph's, wife. William says that he and his brother Wilson discussed this and decided to let all of these secret things be known. It was their thought that the Saints should be made aware that the Prophet was introducing the practice of plural marriage. They also felt that the Saints should be informed of the new doctrine of plurality of gods and that man was a god in embryo, a potential god. That thought was blasphemous to them, and incorrect doctrine.
When it became known that they were establishing the Nauvoo Expositor and the issues began to be circulated, they were threatened by Hyrum Smith and others. The diary suggests that William was threatened unto death. The diary mentions William walking down the street and encountering Hyrum. Hyrum was very angry and threatened him, and others threatened him with guns. A meeting between William Law and Joseph Smith was set up and the Prophet became very angry at him. Then Wilson and William feared for their lives and left in the night. They went to stay at a hotel in Burlington, Iowa.
... While William was in Iowa he wrote that, "I hear that the Smith brothers were murdered. It served them right. They received their just dues. They had it coming." It was at this point that he calls the Prophet the names indicated above-charlatan, false prophet, etc. ...
[Confessions of a Mormon historian : the diaries of Leonard J. Arrington, 1971-1997, Gary James Bergera, editor, Signature Books, 2018]