Thirty-two-year-old Zachary Cope of Lower Makefield Township pleaded guilty, but mentally ill, to third-degree murder in the stabbing death of 53-year-old Rebecca Cope.
He was ordered to spend between 10 and 40 years in state prison.
Cope said he stabbed his mother inside the home that they shared in December 2016.
He said he believed that a hired assassin was posing as his mother, and that's why he killed her.
An autopsy revealed Cope's mother suffered more than 70 stab wounds.
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