 The two argued cases defending the rights of Mormon settlers in Jackson County, served Northwest Missouri in Missouri's General Assembly, and labored for the addition of the Platte Purchase to Missouri's boundaries.In October 1838, the two were ordered by Governor Lilburn Boggs to arrest Mormon prophet Joseph Smith Jr. at the Far West settlement in Caldwell County.Immediately after the conclusion of the Mormon War, Smith and other Mormon leaders were incarcerated at the Liberty Jail for the winter as Doniphan labored for a quicker trial date.