DOYLESTOWN, Pa. (AP) - A Pennsylvania man has pleaded guilty 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 pleaded guilty Tuesday to first-degree murder 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, Sarah Packer, is expected to testify against Sullivan during the penalty phase of his trial. Officials say she intends to plead guilty in the case.

  

Prosecutors have said that Sarah Packer, a former foster parent and child welfare worker, watched Sullivan act out a rape-murder fantasy they shared. The couple allegedly stored the girl's body in cat litter for months, then dumped it in a remote area.