A Pennsylvania man and woman raped and dismembered the woman’s adoptive daughter as part of a disturbed “fantasy,” police said this weekend. Then the couple collected the teenager’s Social Security payments for months, profiting off her death.

14-year-old Grace Packer went missing from her Abington, Pennsylvania home in July. Her adoptive mother Sara Packer told police that Grace had stolen $300 and run away. But the adoptive mother’s sob story didn’t add up, police said. After hunters found Grace’s head and torso in the woods on Halloween, investigators narrowed their focus on Sara. And when she and her boyfriend overdosed as part of a failed suicide pact on December 30, the boyfriend allegedly told hospital workers that he and Sara had committed the sickening murder together.

Jacob Sullivan, 44, and Sarah Packer, 41, were arrested Saturday on a litany of charges including homicide, rape, and abuse of a corpse. The pair had allegedly planned the crime for nearly a year.

"This was a sexual fantasy that was shared between Jacob Sullivan and Sara Packer, and Grace Packer was the object of that rape-murder fantasy," Bucks County District Attorney Matthew Weintraub told media Sunday morning.

The pair finally carried out their plot on July 8, a charging document for Sullivan alleges. That evening, Grace had fallen asleep in the couple’s car on the way to their home. Once they arrived at the house, the couple allegedly beat the teenager and took her to a third-floor attic. There, Sullivan allegedly raped Grace while Sara watched.

Then the pair allegedly attempted to murder the child. Earlier that day, Sara had purchased multiple medications at a local Target, credit card records included in Sullivan’s charging document show. After Sullivan’s assault, Sara allegedly fed Grace the medications, telling her it would ease the pain of the attack. When Grace vomited the pills, the couple made her take them again.

“Following this, she was bound, gagged, and left to die in a cedar closet in [the] 3rd floor attic,” the charging document alleges. “Jacob Sullivan described the attic as extremely hot.”

The couple abandoned the home and the girl, allegedly expecting to find Grace “dead from the effects from the assault, the drugging, and the excessive heat,” police charge. Instead, when they returned to the attic at three in the morning, they found Grace alive and conscious.

Sullivan allegedly strangled her to death with his hands. “It was more physical and took much longer than he expected,” he allegedly confessed to police.

It took two days for Sara to report Grace missing. On July 11, she told police that Grace had disappeared after an argument, taking $300 with her. She described Grace as a troubled child with “behavioral disorders,” who would act out if she did not get her way, and sometimes left the home for “days at a time”. Their latest argument had been begun when Grace asked to visit a friend’s house, Sara told police. When pressed, she could not provide the friend’s name.

But while Sara was describing her daughter as a troubled runaway, the girl was really dead in the attic, police say. After Grace’s murder, Sara and Sullivan allegedly packed her body in cat litter to disguise the smell.

Police added Grace’s information to a missing persons database. But her mother was unusually uncooperative, refusing to return multiple calls from investigators. Sara was also a prolific Facebook user, “so frequent that she will sometimes post about insignificant or minor incidents in her life, such as having a migraine headache,” a charging document reads. But Sara “never posted anything about her daughter being missing.”

She also allegedly continued to collect thousands of dollars in disability benefits from her missing daughter.

"After they murdered her, they maintained the pretense of Grace being alive so that they could continue to profit off of her existence," Weintraub the district attorney alleged on Sunday.

Police discovered that, while Sara had enrolled Grace’s younger brother in a new school that summer, she had made no effort to enroll Grace. It was as though she knew her daughter would never return.

The lack of information led police to revisit Sara’s home for a follow-up investigation October. They did not discover the horrific scene hidden in the attic, but their visit was enough to make Sara and Sullivan nervous. Sara’s credit card records show that she purchased a bow saw several days after police visited the home.

Then on Halloween, hunters discovered Grace’s head and torso in a wooded area. She had not been buried. Cadaver dogs later found her arms and legs. Investigators concluded that she had been killed and stored elsewhere. Her wounds showed the marks of a bow saw, and were full of cat litter.

Inconsistencies continued to appear in Sara’s testimonies. She allegedly went months without providing information requested by police, and gave conflicting information regarding her daughter’s disappearance. She was charged with child endangerment and obstructing an investigation in November.

Meanwhile, Grace’s birth mother had followed the search for her daughter, horrified as it became apparent that Sara was actively impeding the search for Grace’s killer.

"She’s never going to get to see her sweet 16," Grace’s biological mother Rose Hunsicker told NBC10 in December, after Sara was charged with obstructing the investigation. "She’s never going to get to see anything."

Hunsicker lost custody of Grace in 2004, and expressed deep reservations with her daughter’s adoptive parents, calling them “evil” people. David Packer, Sara’s husband at the time of Grace’s adoption, pleaded guilty to sexually assaulting a child in 2011.

"How dare they act like better parents than I am," Hunsicker told the station in December, questioning how the Packers ever obtained custody of her child. They caused "the horrible death of a little girl that never should have [happened]," she alleged.

Sara left jail on bail on December 23. She was still not charged with her daughter’s murder, but police appeared be moving in on her and Sullivan. So on December 30, Sara and Sullivan agreed to enter a “suicide pact,” police allege. Sullivan left a note for his children, proclaiming his innocence and denouncing the growing allegations against him.

“Dear babies,” he wrote in a letter obtained by police. “I love you all so much. You are the only people that I have always been able to count on. I’m sorry that I am taking the coward’s way out, but I don’t have any strength left in me. People want to judge and lie and break me down. They have. I can’t exist with Sara in jail and those fucking lying pigs and the whore media have made it impossible for us to live.”

A woman who lived with Sara and Sullivan called 911 that day to report that the pair had overdosed.

"There's are a lot of reasons he would do this,” a transcript of her call reads. “We're … uh God … we're … I don't know if you have watched the news lately … our … someone we were involved with was recently … It's a big mess, It's a big mess and I don't really know how to explain it … but … oh my God."

Sara and Sullivan were taken to a hospital, where both survived and Sullivan told authorities he wished to confess to the killing. He and Sara had planned for nearly a year to rape and kill Grace, he told police. He admitted to dismembering the girl in a bathtub and driving with Sara to dump the remains in the woods in October.

He and Sara have been charged with murder. The investigation into Grace’s death is still ongoing.

"This is one of the most shocking stunning motives I've ever heard of in my career as a prosecutor,” Weintraub said. “It was a cold blooded crime that was calculated and planned with deadly detail.”