Who is Richard "Ricky" M. Knapp from Under the Banner of Heaven: A Story of Violent Faith and what is their importance?

Ricky Knapp is a drifter who happens to be traveling with Ron and Dan the summer that they murder Brenda and Erica. He is one of two men sitting in the car outside Allen and Brenda's apartment when Ron and Dan commit the murders. Dan meets Knapp while the two are working together on a construction site in Wichita, Kansas. Knapp has just gotten out of jail and has no place to stay so Dan offers to let him sleep in the Impala with him. Knapp takes Dan to a marijuana field where they collect a bag of low grade marijuana that they take with them on the remainder of their road trip. Knapp leaves with Carnes and abandons the Lafferty brothers at the motel after the murders are committed.