Was Alton Nolen mentally ill when he beheaded a female co-worker and tried to behead a second woman at a food plant in Oklahoma on Sept. 25, 2014, or was he simply being a good Muslim by following the dictates of the Quran?

That's the issue the jury will have to decide in the 33-year-old Muslim convert's trial, which opened last week and continued Monday in Norman, Oklahoma.

Nolen told police in 2014 he beheaded his co-worker, Colleen Hufford, and tried to behead another woman at the plant because he felt "oppressed" as a Muslim.

"You know all I was doing was ... what I was supposed to do as a Muslim," Nolen said. "It's in the Quran."

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There were reports at after the incident that Nolen had tried to convert several of his co-workers to Islam and they were not receptive, which may have fueled his rage.

Nolen's court-appointed attorneys are now asking the jury to find him not guilty by reason of insanity. They argued he is mentally ill and believed what he was doing was right because of "delusional misinterpretations of Islamic teachings," according to the Oklahoman, a local newspaper covering the trial.

An expert witness took the stand Monday on behalf of the defense and told the jury that the Quran contains no instructions for Muslims kill unbelievers by beheading unless it is a time of war.

"It does not exist," said Robert Hunt, a professor at Southern Methodist University who calls himself an expert on Islamic beliefs.

For Nolen to believe otherwise makes him insane, according to the defense.

Others would argue that Nolen is perfectly sane because he was doing exactly as the Quran instructs – no delusions required.

In fact, the district attorney argued just that on Monday, pressing the "expert" professor on whether he thought ISIS fighters were insane when they beheaded men and boys. Or what about Boko Haram in Nigeria, or al-Shabab in Somalia? Are they all insane?

The SMU professor responded saying Nolan's beliefs about his Islamic faith are "novel."

Philip Haney, a retired Homeland Security expert on Islamic doctrine and an Arabic speaker, told WND that Professor Hunt of Southern Methodist is clearly under his own delusion about the teachings of the Quran and was doing a disservice by trying to mislead the jury on what devout Muslims are taught in many mosques.

And Nolen is very devout. From his prison photo it is clear that he prays five times a day in the required prostrate position, which is evidenced by the Zabiba or small bruise on his forehead. This is the mark of a devout believer in Islam.

"The blindness of [the SMU professor] is astonishing. Mr. Nolen is not just randomly pulling these doctrines out of the air, this guy is a dedicated Muslim," Haney said.

The FBI interviewers were seeking to determine if anyone had taught Nolen that beheading an "oppressor" is acceptable or may have guided him to those beliefs.

“Uh, no,” Nolen responded. “I read the Quran. Like I say, the Quran is easy to understand. … No one guides me but Allah.”

What Nolen appears to be referring to is Quran verse 2:191 about the "fitnah," which is Arabic for an "oppression" or "persecution" brought on by an unbeliever, meaning a non-Muslim.

Sura 2:291 states:

"And slay them wherever ye catch them, and turn them out from where they have Turned you out; for tumult and oppression are worse than slaughter; but fight them not at the Sacred Mosque, unless they (first) fight you there; but if they fight you, slay them. Such is the reward of those who suppress faith."

Nolen felt like certain co-workers were suppressing his faith, Haney said.

Nolen, who worked at the Vaughan Foods food-processing plant in Moore, Oklahoma, is accused of beheading Hufford, 54, and attempting to behead Traci Johnson, 43.

Johnson's life was saved when Mark Vaughan, the chief operating officer of the company and a reserve sheriff's deputy, shot and wounded Nolen as he repeatedly stabbed Johnson, according to testimony at the trial.

Nolen is charged with first-degree murder and assault and battery with a deadly weapon. He may also face federal charges if the Justice Department decides his attack was an act of terrorism.

Nolen was interviewed twice at the hospital while recovering from his gunshot wounds.

In the first interview, he admitted to the FBI that he regularly watched Islamic beheadings on YouTube, including those done by the Islamic State of Iraq and Syria.

The attack brought national attention in 2014, but three years later no national media outlets seem to be giving the trial primetime coverage.

"Mainstream media is not doing their job," Haney said. "They should be covering this trial and asking, 'What do you mean by oppression? What is this concept and where is it in the Quran? What is the source of what he says he believes in ... instead of these vague statements that he is oppressed? Where is the natural curiosity of the press? For the press, that's like an atomic nitro glycerin. When a devout Muslim who is Shariah-compliant says he's oppressed, you're watching a ticking bomb. This guy is a convert. How on earth did he pick up that Quranic concept so quickly? He just swallowed it up like a sponge, this view that some other worldview is oppressing him. And then you have the Muslim community telling him he has the right to lash out like he did, to kill them, if they are oppressing you."

Assigning the violence of Muslims to mental illness is the knee-jerk reaction of today's media and most law enforcement, he said.

"That's just another way to gloss over the truth," Haney said. "People are going to scream about it and say that's not true, so we're going to miss these warning signals [from potential terrorists]."