I just wanted to share some personal knowledge of this. My brother has Asperger's, OCD, anxiety and depression. He is 32 he is my younger brother. He is quite slight of stature, but he can be and has been very violent. He has destroyed his apartment on several occassions. He is a very lonely individual. When he was younger there was not alot known about this disorder (especially where we lived) and he didn't get many of the early interventions that are now available. We also spent many years estranged, not because I wanted to, but because I did not understand him or how to talk to him. We have come a long way from that, but he still has angry and violent outbursts. They are usually very impulsive and short-lived.
I say this with a very heavy heart, as I am sure that most of these individuals, particularily those who have family on this board are NOT this way. BUT, it is possible. One thing about my brother is that he has told me numerous times how jealous he is of me. He wishes he had friends and a spouse, and children like I do. So, I am thinking this has all the hallmarks of a jealous rage/revenge type fantasy. With my brother, he also has a savant quality where he can latch onto one or two things and be very knowledgeable about the subject. I wonder if the guns/shooting were some sort of hobby his mother and him enjoyed together and it became a sort of obsession (OCD) whereby he plotted this out of many months, possibly fantasizing about it, and there must have been a precipitating event that set his fantasy/plan into action.
Please understand this is all my own opinion, based on my life experiences and in NO WAY am I lumping all individuals with these issues into this scenario.