you do not have a good explanation of this event. it's loners; it's masculinity; it's guns; it's relativism; it's video games; its militarism; it's mental health. perhaps it's all these things and a lot lot more. how fast you got to an explanation is a measure of how hard something like this for you to face. well, it is hard to face. but even as we figure out what happened etc, this event needs to retain a penumbra of incomprehensibility that hints that we are unknowable to ourselves; you must not deprive an event like this of its excess; you have to try to hold on to a feeling of being overwhelmed or disassembled in the face of this. the disorientation you felt before you remembered 'guns!' is the right response. you have to not figure it out, quite, and you have to keep trying, or else you have betrayed it and yourself.