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

Richard, better known as Ricky Knapp, was a drifter who happened to be traveling with Ron and Dan the summer they murdered Brenda and Erica. He was sitting in a car outside of Allen and Brenda's apartment when the murders were committed. He and Carnes leave the Lafferty's right after the murder.