The media reported that his family moved to florida a year before his mother died. Also, the bit about it being a failed relationship does not appear to pan out as he was apparently living with a woman and LE spoke with her. You can discard the bully theory as well, since (again, from news reports) he was allegedly well-liked by both faculty and students.
That being said, I noticed the dad said he was a diabetic. Untreated diabetes (he was allegedly off his meds) can result in severe depression and sometimes, even hallucination. Iow if that is what happened...