Doctors told a Fort Worth court Brent Bartel, 40, was a paranoid schizophrenic, the Fort Worth (Texas) Star-Telegraph reported Friday.
Police said Bartel used a box cutter to cut a pentagram into his 6-year-old son's back in December 2012 at the family home in the suburb of Richland Hills.
The boy was treated at a local hospital.
Bartel has been found incompetent to stand trial two other times since his arrest. In November, he was sent to a hospital in Vernon for treatment, but he refused to take his prescribed psychoactive medications.
An evaluation by Dr. Timothy Nyberg in January said Bartel made bizarre religious assertions and that the patient couldn't discuss his case without mentioning bizarre religious ideas.