Doubt anyone can. The lobby is too strong to break, so far. And the culture has become desensitized. It's not "omygod there's been a mass shooting" anymore, it's more of "how many this time" as if it cannot be changed, but must only be endured.
That being said, in this case it's not the guns, it's the guy. (It pains me to say that, but if he hadn't had a semi-automatic, I think he'd have used dynamite, like when that guy in the upper-midwest blew up the school full of children to settle his grudge.)
I have not followed this closely; however, what I heard was it was one male shooter. He opened fire at a church building, then in the church. He meant to frighten first and then kill - this was one mean bastard with a grudge. My guess is that he has/had a history of violence and of being a bully.
If I might conjecture from what I know of Texas (having grown up there) and human nature: This will be a white male, young-to-middle-aged, probably not terribly highly educated, and pretty much a failure in life. His wife/girlfriend will have left him very recently and/or he will be in the middle of an ugly custody battle. His wife and/or her family (or possibly his own children, if he has any) will be members of that church. He intended to cause as much pain to them as he possibly could. This is the kind of guy who would kill his own kids, rather than have his ex have custody and him have to pay child support - with the added bonus of him knowing it would gut his ex to have her children dead.
I believe I heard in passing that the shooter ran away when confronted by another armed individual after he shot up the interior of the church. That tells me he was not suicidal, but intended to make a get-away. He is now dead. If it was from the bullet of the civilian who confronted him, there will be a medal/commendation awarded to the gent who shot him. If it was from a self-inflicted shot, he's just dead. Along with all those others.
In any case, unless he's posted a rant somewhere or left a note, which I doubt (as I think he meant to live afterwards), all Law Enforcement and anyone else will be able to do is try to guess what the hell went so wrong with this guy. It'll be in the news for a while, then die down as people go back to their daily lives. Except for the ones who have lost their loved ones, and the dead.
There's nothing but sad around this. Nothing to say that will help, nothing one can do to change history. I'll be lighting a candle for them again tonight. So, so sad.