He was schizophrenic, hearing things, was talked to by his microwave.
All started supposedly because he had PTS from being in 9/11 and had an altercation with a man on a plane. After that, he felt this man had put agents to stalk him. However, that does not justify why he was able to purchase firearms after being discharged for his aggressive PTS. They all agreed that he shouldn't have been able to purchase firearms. Did not show up on background check? Or maybe the background checkers multisensory integration was manipulated via remote tDCS and therefore could not see what was on the background check. Perhaps he was compelled to get the guns and attack his station because he was being stalked. He wasn't being payed promptly in his new job, a mistake in the department, so clearly mind control did it. A collaboration of tricks of the mind to result in terror.