In a calm, emotionless voice, Sara Packer described watching her boyfriend murder her 14-year-old daughter, Grace, in 2016.

She admitted to participating in the crime — the kidnapping, rape, killing, dismemberment, and disposal of an adopted child she said she thought of as “a nonentity." Packer said she and Jacob Sullivan didn’t initially plan to kill the girl, rather to keep her in the attic for Sullivan to rape at will. But in the end, she said, Sullivan panicked.

“I think the reality of what he had done set in, and there was no going back,” Packer said. “So he decided it was time for her to die.”

Packer’s testimony marked the first time she had spoken publicly about the crimes. She took the stand on the fourth day of Sullivan’s sentencing hearing, a perhaps-two-week proceeding at the end of which a jury will determine whether he is sentenced to death or life in prison without the possibility of parole.

Sullivan, 46, pleaded guilty last month. Packer, 44, who worked for foster care and adoption agencies, had already struck a deal with prosecutors, agreeing to cooperate with them in exchange for a life sentence. She is expected to plead guilty after Sullivan is sentenced.

Sullivan’s attorneys called her to testify Wednesday in an attempt to bolster their argument that she manipulated Sullivan into brutalizing and ultimately murdering Grace and that as a result, Sullivan shouldn’t be sentenced to death.

But on the stand, Packer said Sullivan was the dominant force in the teenager’s killing.

“She didn’t have to die," Packer said. “I got wrapped up in Jake’s fantasy, and I didn’t think I could tell him no without losing him."

Earlier in the day, Grace’s other relatives had described her as a bright, bubbly young girl with an infectious “little-girl giggle" who loved hip hop and country music, swimming, and the summertime.

But her mother saw her differently, as “a difficult child” who often acted out and needed to be punished.

“Grace had become, for lack of a better word, a nonentity,” Packer said. "I wanted her to go away.”

Packer, with thin red hair and wearing a red prison jumpsuit, spoke slowly and deliberately, at times taking long pauses before answering attorneys’ questions. At one point, Bucks County Court Judge Diane E. Gibbons loudly told her, “Answer the question.”

From behind glasses, Packer’s eyes darted around the room, never resting on Sullivan, who sat at the defense table and dabbed his eyes at the beginning of her testimony.

When Packer and Sullivan first met in 2013, she said, Sullivan was her daughter’s “biggest advocate." But over time, Packer said, she “educated” Sullivan, showing him how hard the child was to parent.

After Sullivan moved in with Packer, she said, she began grooming him to assault Grace in the same way she had groomed her ex-husband, David Packer, to assault a child she had fostered.

By July 2016, Packer said, she had “given up” on the teen. For weeks, Packer said, she had been secretly putting medication in her daughter’s pudding “to make her compliant, make her groggy." She did so one last time on July 7, she said, before she and Sullivan took Grace from a home they rented in Abington to another rental property near Quakertown.

There, she said, Sullivan punched Grace in the face and raped her as Packer watched.

During the attack, she said, Grace looked to her, and she told her, “I can’t help you anymore. This is now your life.”

The couple drugged Grace, bound her with zip ties, put a ball gag in her mouth, and left her in an attic closet to die in the summer heat.

Before Sullivan and Packer returned the next morning, she broke free of the zip ties and spit out the ball gag, prosecutors said. Seeing this, Sullivan grabbed her from behind, put her in a choke hold, and suffocated her, telling her, “Just go, honey, just go,” he told authorities in confession tapes played in court Tuesday.

Packer said her daughter looked to her in the moments before she died.

“I took her hand and told her it was OK to go,” Packer said. “It seemed like it took forever, but it was only a couple minutes.”

District Attorney Matthew Weintraub replied: “How do you think it felt for Grace?”

“Probably, like, forever," Packer said.

Packer said it was her idea to buy kitty litter to store Grace’s body in. They kept the remains in the attic, in a cardboard box surrounded by boxes of Sullivan’s comic books, until authorities arrived at the home in October to follow up on her report that the girl had gone missing.

Then, Packer said, she went out and purchased a bow saw for a “dual purpose” — cutting firewood and dismembering her daughter’s body.

In an upstairs bathroom, she said, she and Sullivan cut up Grace’s remains, then drove 75 miles to Luzerne County and dumped them in woods, where they were found by hunters on Halloween.

Even after the body was discovered, Packer said, she was “fairly confident” that they’d get away with the crime but had to keep reassuring Sullivan, telling him, “Everything will be OK.”

The couple agreed not to search on the internet for anything related to the killing, and she hid news stories from Sullivan so as not to “upset him.”

As the police investigation ramped up and media attention intensified, Sullivan and Packer attempted suicide, but survived. In the intensive-care unit at the hospital, Sullivan confessed to hospital staff, and later police, that he had killed Grace, whom he called a “nightmare.”

Packer told authorities that Sullivan’s confession made her "feel betrayed.”

Weintraub called Packer “an utter, miserable failure" as a parent and human being.

In a victim-impact letter read in court, Grace’s 14-year-old brother asked that his sister be remembered beyond the gruesome details of her death, and that measures be taken to protect other children from abuse.

“I want you to find a way to watch out for all kids," he wrote to the court. “Please, this will help me heal.”