The child's adoptive mother has agreed to plead guilty in exchange for a life sentence.

DOYLESTOWN, Pa. (AP) — Family members of a slain 14-year-old girl said Thursday they remain haunted by her torture and excruciating death, describing for jurors their unrelenting pain at a hearing that will determine whether her killer will be sentenced to life or death.

Jacob Sullivan, 46, pleaded guilty in the 2016 rape, murder and dismemberment of his girlfriend's daughter, Grace Packer. Grace's adoptive mother, Sara Packer, has agreed to plead guilty in exchange for a life sentence.

Prosecutors have said Sara Packer hated Grace, shared a rape-murder fantasy with Sullivan, watched as he sexually assaulted and strangled her in a hot attic outside Philadelphia, and helped hack up her body and dispose of it months later.

Sara Packer took the stand Wednesday and said Grace had a tendency to be a "very difficult child."

The defense has said that Sullivan should get the same sentence as Packer — life in prison.

Sara Packer, who wore a red prison jumpsuit, also said she has a degree in psychology and an IQ over 140.

"It sickens me to know that Grace was abused, tortured and literally thrown away like she was a piece of trash," her cousin, Karie Heisserer, with whom Grace lived for a time in 2015, said in court Thursday. "Grace is in a better place now, free from evil and pain."

Jurors saw photos of the bubbly but troubled teen in happier times: Sitting in the cab of her uncle's big rig, frolicking in the sand at her first trip to the beach, delighting in birthday cake at a pool party. But all of that happened with relatives, not with Sara Packer, a former county adoptions supervisor who prosecutors say spent years physically and mentally abusing the little girl she fostered and then adopted.

Bucks County District Attorney Matthew Weintraub told the jury Thursday that he agreed to a life sentence for Sara in exchange for her confession and guilty plea because the physical evidence against her was weak, because it was Sullivan who raped and killed Grace, and because her crimes did not qualify for the death penalty.

In a confession to police, Sullivan said he and Sara Packer plotted Grace's death. Sullivan admitted he punched and raped Grace as Sara Packer watched, bound her hands and feet with zip ties and stuffed a ball gag in her mouth. Prosecutors said Sullivan and Packer also gave her what they intended to be a lethal dose of over-the-counter medication and left her to die in a sweltering attic.

Grace eventually managed to escape some of her bindings and spit the gag out, but was unable to make it out of the house before Sullivan and Packer returned overnight — some 12 hours later — and Sullivan strangled her as Sara Packer looked on.

The couple stored her body in cat litter for months, then hacked it up and dumped it in a remote area where hunters found it in October 2016, prosecutors said.

Grace's younger brother, Josh Packer, now 14, told jurors the only way he can bear his loss is if adults know her story and then act to prevent child abuse.

He said in a statement read by a detective that if his big sister was told she could save other kids' lives by giving her own, she would ask, "What do I have to do?"

"Watch out for all the kids so that a loss like Grace's loss never happens again," Josh wrote. "Do your best to help kids who can't help themselves."

That's not what happened in Grace's case.

Sara Packer and her husband at the time, David Packer, adopted Grace and Josh in 2007. The couple cared for dozens of foster children before David Packer was sent to prison for sexually assaulting Grace and a 15-year-old foster daughter at their Allentown home, about an hour outside Philadelphia.

Sara Packer lost her job as a Northampton County adoptions supervisor in 2010 and was barred from taking in any more foster children. But child welfare authorities did not remove Grace from the home, despite evidence of abuse.

The Pennsylvania Department of Human Services launched an investigation after Grace's murder but its findings have not been made public.

