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An adoptive mother and her boyfriend were arrested after the woman’s 14-year-old daughter was brutally beaten, raped, killed and dismembered in what prosecutors in Bucks County, Pennsylvania, on Sunday called a “rape-murder fantasy.”

Jacob Sullivan, 44, was arrested Saturday after allegedly confessing to killing Grace Packer, whose remains were found by two hunters last Halloween in a wooded area in Bear Creek Township, according to a news release from the Bucks County District Attorney’s Office.

Grace had been reported missing in July 2016 in Montgomery County by her adoptive mother, Sara Packer, who said the teen had disappeared after likely running away, the release stated.

After his arrest, Sullivan allegedly revealed to detectives that the teen was assaulted over the course of 18 hours and killed, according to a probable cause affidavit. The couple — accused of conspiring to beat, rape, poison and strangle the girl — had allegedly plotted the teen’s slaying since Grace returned from a stay with extended family at the end of 2015.

In an interview with detectives, Sullivan said he and Packer drove a sleepy and pajama-clad Grace from their home in Abington to a new residence in Richland Township on the morning of July 8, 2016, the release stated.

When they entered the house, Sullivan struck Grace several times in the face, then took her to the third floor where he allegedly raped Grace in front of Packer, who stood by and watched, according to prosecutors.

Packer left to buy Tylenol PM and other drugs in order to sedate the teen, telling her the pills would “minimize her pain from assaults.” After, the couple gave her an overdose amount of drugs, then bound and gagged her, Sullivan told investigators, according to the release.

The teen was left alone to die in the hot attic, but she was still alive at 3 a.m. the following day, when the couple returned to the house. Sullivan then allegedly told detectives  killed the teen by strangling and suffocating her.

Grace suffered terribly before she died, according to Bucks County District Attorney Matthew D. Weintraub, who called her slaying “a rape-murder fantasy that was shared by Jacob Sullivan and Sara Packer, and they acted it out.”

After the teen died, Sullivan and Packer put her body in cat litter to mask the odor, leaving it in the attic for about three months before dismembering and dumping her remains, prosecutors said. The body was found without arms and legs.

According to the probable cause affidavit, Sara Packer was filmed buying a bow saw and two extra blades at a tractor supply store. A forensic anthropologist who examined the body determined scarring and tool marks on her bones were made by a blade similar to the one Packer bought, the release stated.

Three days after the teen was killed, Sara Packer reported to police that Grace was missing.

Over the weekend, Sullivan was arrested on charges of homicide, rape, involuntary deviate sexual intercourse, unlawful restraint, kidnapping, possessing instruments of crime, endangering the welfare of a child, abuse of a corpse, simple assault, tampering with physical evidence, and corresponding conspiracy charges, the release stated.

Packer, meanwhile, was arrested hours after Sullivan on suspicion of homicide, kidnapping, unlawful restraint, possessing instruments of crime, endangering the welfare of a child, abuse of corpse, simple assault, tampering with physical evidence, and conspiracy to commit rape, and each of the above crimes, according to the release.

“Unfortunately, Grace Packer was a disposable child to these people,” Weintraub said of the girl, who was taken in as a foster child by Packer at the age of 3 and adopted by the woman now charged in her killing.

“Who will now speak for Grace Packer? We will,” Weintraub added.

The alleged crimes could warrant the death penalty, he said.

Sullivan had been hospitalized since late December, when he allegedly overdosed on prescription drugs as part of an alleged suicide pact with Packer and was found unresponsive at his home. Packer, 41, was also found unresponsive the same day, according to the affidavit.

Both have been denied bail and remain behind bars.