An Oklahoma judge is scheduled to decide whether a man accused of fatally stabbing his father, the state's former labor commissioner, is mentally competent to plead guilty to a first-degree murder charge.

Prosecutors say Christian Costello repeatedly stabbed his father, Mark Costello, at an Oklahoma City restaurant on Aug. 23, 2015. Christian Costello has pleaded not guilty.

District Judge Ray Elliott ordered a competency evaluation in May after Christian Costello said he wanted to change his plea. Costello's attorney, Bob Ravitz, has said he has a history of mental illness and that he believes Costello was legally insane and did not know right from wrong when he attacked his father.

The competency hearing is scheduled for Wednesday in Oklahoma County.