Who is Nash from Lullaby: A Novel and what is their importance?

Nash is a paramedic. Streator works with Nash while he is gathering information for his sudden infant death stories. Over the course of the story, Nash confesses that he would like to have sex with a beautiful woman found dead in a hotel room. From this confession, Streator deducts that a rash of dead fashion models are the result of Nash's sick compulsions. Streator later confronts Nash and kills him in a quick draw using the culling song.