It's the timing of all this that confuses me.
- 11:59 - the police are first called. I'm assuming this when he was interrupted while rummaging through the bag and thrown out of the store
- 12:27 - the police are called again, with a report that he was threatening the store employees
- 12:47 - the police arrive, he stabs one with a screwdriver and is shot by the other officer and three store employees
This isn't a "he did something stupid in a moment of stupidity" thing. Why was he still there, half-an-hour after he'd been thrown out? And still still there twenty minutes after the cops were called the second time?
This feels more like a psychotic break than either an impulsive or a premeditated crime.