First of all nothing excuses this and my condolences to the families of these people and anyone injured I hope makes a speedy recovery.
Now one thing that has struck me as odd in this case is that the alleged shooter is ex military and worked at Fort Bragg in the Psychological operations unit, now call me really paranoid but the army base has a history of shootings the most notable being that by Major Hasan (allegedly) a psychiatrist, the Aurora shootings again allegedly by person who had been taking a doctorate in neuroscience.
Either anyone studying or practicing these related fields is a threat and they should ban the subjects or there are three Manchurian candidates wandering around. Or there were just have three random shootings for no apparent reason. I expect you will see more such “random” mass shootings until the government gets it’s way and a gun ban is enforced. Then oddly these incidents will suddenly stop.