A Pennsylvania man pleaded guilty on Tuesday in the rape, murder and dismemberment of a 14-year-old girl, and the victim's adoptive mother has agreed to plead guilty and serve a life sentence.

Jacob Sullivan, 46, pleaded guilty to all charges in the 2016 death of Grace Packer. A jury outside Philadelphia will determine a sentence of either life in prison or death.

Grace's adoptive mother, Sara Packer, 44, is expected to testify against Sullivan during the penalty phase of his trial. Packer has agreed to plead guilty in exchange for a life sentence, according to her attorney, Keith Williams.

Sullivan was Sara's boyfriend.

Prosecutors have said that Sara Packer, a former foster parent and county adoptions supervisor, watched Sullivan act out a rape-murder fantasy they shared.

Sullivan's plea hearing was interrupted Tuesday afternoon after he fell ill and was taken to a hospital. The hearing is scheduled to resume Wednesday.

Grace's death raised questions about whether child welfare agencies could have done more to protect her. Packer and her husband at the time, David Packer, cared for dozens of foster children before David was arrested in 2010 and sent to prison for sexually assaulting Grace and a 15-year-old foster daughter at their home in Allentown, about an hour north of Philadelphia. She lost her job as a Northampton County adoptions supervisor in 2010 and was barred from taking in any more foster children.

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

Sullivan beat and raped Grace, and she was bound, gagged and left to die in a sweltering attic, authorities have said. Returning the next day and finding Grace was still alive, Sullivan strangled her, court documents said. 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, police have said.

Sullivan, whose attorney had said Sarah Packer masterminded the killing , entered his plea as jury selection was about to get underway. Packer's trial was expected to begin next month.

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This story has been corrected to show Grace Packer's adoptive mother is Sara Packer, not Sarah Packer.