Authorities said Jacob Sullivan never finished pleading to the all the charges because of a blood pressure spike.
He was sent to the hospital and will be back in court tomorrow, according to officials.
Sullivan was charged with first-degree murder in the 2016 incident in Quakertown.
The teen's adoptive mother, Sara Packer, is expected to testify against Sullivan during the penalty phase of his trial.
She's also expected to plead guilty in the case.
Prosecutors have said that Sara Packer, a former foster parent and child welfare worker, watched Sullivan act out a rape-murder fantasy.
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