The one thing I'm surprised at by reading this thread, is how the viewpoints of many differ in so many ways. Obviously, this chap was considerably disturbed by something in his life, that significantly impaired normal thinking. It doesn't mean however, that because he was thinking irrationally, that he wasn't capable of carrying out rational tasks. For example, he got to the airport without incident (we assume).
In accessing the aircraft, for which he had the requisite permitted company clearance, and with the job he had, he would have been familiar with at least the basic operations of the Q400, and most definitely would have been familiar with the cockpit layout and "what bits do what".
I agree that an airline pilot type-rated on the Q400, is a very professional post. I disagree that only a fully-trained, fully-qualified, type-rated person is capable in any capacity to get a Q400, or any commercial aircraft airborne.
Here's where I'm likely to draw comments taking my post out of context.... regardless of aircraft type, and the complexities of electronic systems - the basic principles of flight remain the same.