Who is the Fat biker and what is their involvement in the slasher case?

The Fat biker's identity is revealed and readers learn it is Martha Surtees, Jamey's nurse. Surtees is part of an outlaw biker gang called the Ghouls. She was arrested for second degree murder and was put in jail until Souza was able to free her. While she was in jail, she studied to become a nurse. Surtees is the one who physically poisoned Jamey.