Investigators say Fagan was the suspect in an ongoing criminal investigation involving one of Cathy Paternoster's three daughters, but would not elaborate. Fagan also had a relationship with Paternoster's mother, Betty Paternoster.
Authorities believe Fagan committed the killing so that Paternoster's mother, Betty, would obtain custody of her granddaughter.
Fagan is being held without bail in Rancho Cucamonga.
Fagan is the author of "Cast Your Net: A Step-by-Step Guide to Finding Your Soulmate on the Internet."
