By Jon Jordan, NEWS 9

OKLAHOMA CITY -- A Nichols Hills doctor accused of killing his 9-year-old son is expected to be formally charged this week.

Dr. Stephen Wolf remains in the Oklahoma County jail. Police have alleged that Wolf fatally stabbed his son, Tommy, and cut his wife at their home in Nichols Hills on Nov. 16.

According to an arrest affidavit, Wolf repeatedly told the police officer who stopped the attack that his son had "the devil in him."

A week later, those who've known Dr. Stephen Wolf for years still can't believe what he's accused of doing.

"The Steve Wolf I knew was not this Steve Wolf," said long time family friend Bill Cathey.

And if friends are right and Doctor Wolf was not himself, it's believed his legal defense will recommend he pleads not guilty by reason of insanity.

"The issue of temporary insanity is certainly a viable defense and would be raised at some point and time," said NEWS 9 legal analyst Irven Box.

Irven Box points not just to Dr. Wolf's alleged actions the night of the murder, but his mental history laid out in documents with the Oklahoma Medical Board which shows Wolf at times suffered from major depression.

"I suspect he will meet your legal criteria for insanity," said Forensics Psychiatrist Lawson Bernstein. "Whether that's successful remains to be seen."

Doctor Bernstein said based on what he's seen Wolf's mental problems likely go beyond just depression. Bernstein suspects he was psychotic when he killed his son, and if a jury agrees, he believes there's a future for Wolf beyond just the walls of psychiatric facility.

"This is not some serial killer and this is his fourth homicide. So if I'm correct that he was psychiatrically ill when he committed this crime, once under treatment there's a very good chance that he will get better and with appropriate treatment stay well," said Dr. Bernstein said.

Now while Irven Box assumes the insanity plea would be used, he said first it's going to have be determined that Wolf is even competent enough to stand trial.