This latest shooting is probably just another case of untreated male depression. Probably a good hunk of shooting deaths in the States is due to this. He was about the age when it hits. Perhaps the wife was abused, but Bonny and Clyde pairings have happened before.
In the terrorist belts, there is a whole infrastructure dedicated to finding these suicidal depressives, and equipping them. In the States, none of that is necessary. As soon as the person snaps, he can accumulate all the weapons he needs. There are millions of people with enough stuff in their basements to wipe out a small town.
As a depressive myself, I think there are two things that make the situation worse. First, Hollywood glories in untreated depression. Look at all the latest movies! It wouldn't be a story if the person just got a little pill and was all better. Depression is good, and even better if you go out and kill people. Of course, it's always 'bad' people they kill.
And of course, there's the other thing. Each year lots of people step in front of subway trains, but that lacks satisfaction in the planning. Far better to get a gun. Perhaps a lot of them. What are you going to do with all these guns? Big boxes of ammo are glorious. Out to kill bad people! Everybody who wants to live is bad.
We'd be better off if we had a culture of recognizing the symptoms and then getting people the little pills. There should be no stigma to realizing you need a little help. But until that happens we'll see more and more killings, and it has nothing to do with radical terrorism.
Addition: From an earthquake perspective, one has to determine if this has the potential to go exponential, that is, an ever-increasing rate of mass shootings, with larger impacts. The rate of going suicidal should be steady, since it is a genetic factor. The availability of the Internet is probably saturated, so the culture and material to identify 'bad guys' is steady. Open information might lead to earlier treatment, but I doubt it. That just leaves the ease and cost of accumulating powerful weapons. Cost is going down, and availability is going up in a linear fashion. So it's a tough call, but I think it's weak exponential. So, expect an increasing rate of shootings, with higher impact. That means the graph of 'shooter deaths' could be to the power of 2, just like earthquakes in Oklahoma and the potential of death.