him from speaking. After 1857, he was not living with family and there was speculation by family, friends, and others that he was enslaved again. The 21st-century historians Clifford Brown and Carol Wilson believe it is likely that he died of natural causes, because he was too old to be of interest to slave catchers. According to John R. Smith, in letters written in the 1930s, his father Rev. John L. Smith, a Methodist minister in Vermont, had worked with Northup and former slave Tabbs Gross in the early 1860s, during the Civil War, aiding fugitive slaves on the Underground Railroad. Northup was said to have visited Rev. Smith after Lincoln's Emancipation Proclamation, which was made in January 1863. There is no contemporaneous documentation of his death. It is believed by historians that he died in 1863 or 1864. Historiography Although the memoir is often classified among the genre of slave narratives, the scholar Sam Worley says that it does not fit the standard format of the genre. Northup was assisted in the writing by David Wilson, a white man, and, according to Worley, some believed he would have biased the material. Worley discounted concerns that Wilson was pursuing his own interests in the book. He writes of the memoir: Twelve Years is convincingly Northup's tale and no one else's because of its amazing attention to empirical detail and unwillingness to reduce the complexity of Northup's experience to a stark moral allegory. Northup's biographer, David Fiske, has investigated Northup's role in the book's writing and asserts authenticity of authorship. Northup's full and descriptive account has been used by numerous historians researching slavery. His description of the "Yellow House" (also known as "The Williams Slave Pen"), in view of the Capitol, has helped researchers document the history of slavery in the District of Columbia. Influence among scholars Ulrich B. Phillips, in his Life and Labor in the Old South (Boston, 1929) and American Negro Slavery (New York, 1918), doubted the "authenticity" of most narratives of ex-slaves but termed Northup's memoir "a vivid account of plantation life from the under side". The scholar Kenneth M. Stampp often referred to Northup's memoir in his book on slavery, The Peculiar Institution (New York, 1956). Stanley Elkins in his book, Slavery (Chicago, 1959), like Phillips and Stampp, found Northup's memoir to be of credible historical merit. Since the mid-20th century, the civil rights movement, and