HORSHAM, Pa. (AP) - A police search was conducted at the suburban Philadelphia apartment of a third person of interest in the slaying of a 14-year-old girl as part of a rape-murder fantasy shared by her adoptive mother and her boyfriend.

Detectives from Montgomery and Bucks counties started investigating the Horsham residence shortly before 4 p.m. Tuesday in connection with the death and dismemberment of Grace Packer.Prosecutors say the teen was beaten, raped as her mother watched, poisoned and then strangled hours later. Her dismembered body was discovered in a Luzerne County park on Halloween.Sara Packer and her boyfriend, Jacob Sullivan, face a slew of charges in Grace's death.Police say the woman who lives at the Horsham apartment was involved in a polyamorous relationship with the couple. She hasn't been charged.