Who is Allen Lafferty from Under the Banner of Heaven: A Story of Violent Faith and what is their importance?

Allen Lafferty is the youngest of the Lafferty brothers. He was the only one of the brothers who was not a member of the School of the Prophets. Allen was the husband of Brenda Lafferty and father of Erica. It is indicated that Allen was abusive toward Brenda and that at least one time she had contemplated leaving him. Allen is aware that his brother's removal revelation includes both his wife and his daughter, but does not mention this fact to his wife. Allen is the one who discovers the bodies of both his wife and his daughter after they are killed. When he finds the two, he knows immediately who it was that committed the crime.