Evil vs. Mental illness

Although the priest Sunday morning was about 100 years old, he was talking about how all of the negatives in this world are in relation to the devil. The main topic was of the Colorado shooting just a few weeks ago and how the killer was a form of the devil... If I had a few minutes to spare after I would have told him that I completely disagree. The shooter of the Colorado disaster was mentally ill, not taken over or in a form of the devil. Statements like this make me question my already fragile faith. How could he drain the hundreds of minds sitting before me, under the "voice of God" suggesting that this man was the devil? To me, there needs to be some sort of line between religion and science/evil and mental illness. Please don't get me wrong... what happened in Colorado was tragic and appalling but has nothing, if anything to do with religion. I will remember this as a horrific event that cross country has touched the lives of many, but the people involved will be for the rest of their lives.