I actually anticipated that a religious dumba$$ would immediately claim that James Holmes was "possessed" by evil spirits and that this is why he did what he did. After all, the Bible strongly suggests that mental illnesses are due to the influence of evil spirits which must be exorcised. However, I also expected that many religious people would loudly deny this and attempt to tap dance around the truth of what their religious texts teach. "We're not that backward and stupid," they would have protested.
Unfortunately they are that stupid and backward when it comes to the person of Rev. Longenecker, a Catholic priest from Greenville, SC. It's gratifying to see that official religious nuts are now taking this position, which is certainly consistent with the Vatican's extensive use of exorcism.
The problem is that this actually creates more problems than it solves for religious nutjobs. To begin with, there is really no evidence of possession....but lack of evidence doesn't usually deter them anyway. Holmes wasn't wearing any pentagrams or showing any interest in the occult. All the evidence suggests that he was raised as a Christian, and may have even attended a church in the month or so before the shootings.
Also, if he was "possessed" then it must have been for months, because he appears to have stockpiled these armaments and explosive devices for some time. His journal also indicates that he was planning this for some time. He was also seeing a psychiatrist, who probably would have noted that he his head was spinning and he was reciting the Lord's Prayer backwards.
Holmes showed no signs of worshipping the devil when he was conducting his rampage. Witnesses say he said nothing. He identified himself as a comic book character to police, not Beelzebub. In fact, virtually no serial killer in modern times has claimed to be possessed by the devil. Isn't that odd?
More importantly, if demonic possession is true then it seriously undercuts theologians' frequent, and typically disingenuous arguments about "free will". If Holmes was "possessed" then he was not truly exercising his own will, and could certainly not be held responsible for his actions.
Also the fabrication of "free will" is essential to modern theological excuse-mongering to explain the existence of evil in the world. See, it's not God's fault that evil exists, they claim, because evil is just the result of bad choices that people make with free will. They say that "free will" is so G*ddamn important that God allows genocidal maniacs to butcher others by the thousands or even millions, rather than violate the "sacred" free will of some dictator or serial killer.
But if there are evil entities that can take over the wills of humans then this excuse falls apart. A God who was obsessed with free will at any price surely would not allow for evil spirits who have the power to circumvent human free will at their whim. If he allows that then free will apparently isn't all that important, and we can't use it to explain away so many of the bad things that happen in the world on a daily basis.
Of course, if you accept that mental illness is caused by chemical imbalances, as opposed to primitive superstitions about evil spirits, then you still have a problem for so-called free will. We don't hold insane people responsible for their crimes because they are not in control of their whims to a reasonable degree. Yet again, God apparently just isn't that into free will. So you'll have to find another excuse for God to just shirk all responsibility for preventing terrible events from taking place.