DOYLESTOWN, Pa. — A man diagnosed with schizophrenia has been sentenced to 10 to 40 years in the murder of his mother in their suburban Philadelphia home.

Thirty-two-year-old Zachary Cope pleaded guilty but mentally ill in January to third-degree murder and possession of an instrument of crime.

Authorities in Bucks County said he stabbed 52-year-old Rebecca Cope in December 2016 in the Lower Makefield Township home, then flagged down a motorist to tell him about the crime.

The (Doylestown) Intelligencer reports that authorities said the defendant said he stabbed his mother during an argument about putting olive oil on a cutting board and believed she had “morphed” into an FBI agent “or vice-versa.”

Officials said at Monday’s sentencing that Cope will be credited for time served since his December 2016 arrest.