The kid apparently left a 25-minute confession on his phone. Maybe that will shed some light on why he did it, but I'm not hopeful. He seems to have been an introvert, and hardly political at all. He did leave behind an apparent list of future targets,maybe that will explain some of it.
Interestingly, on the packages he mailed, he gave his name as "Kelly Killmore." Maybe he just wanted to see the world burn.
Onward and upward,
airforce