But here is an article by the Atlantic that I found very interesting.
I myself am very pro-2nd Amendment, having been a competitive rifle shooter.
https://www.theatlantic.com/politics/archive/2016/03/whats-the-solution-to-gun-violence/462537/
I wish I knew how to identify them in advance as I’d happily use my personal firearms to put a bullet in their mangled brain 
While I understand, it is this kind of thinking that leads to a lot of innocent people being targeted. I don't remember who said it - and yes, I think it does apply - I'd rather see 12 guilty men go free than one innocent person go to prison. That to me sums up the legal system in our country. As it should be.
When we try to "identify" those that may be trouble and lock 'em up, that's not what we as a Country stand for. So I see the point of law-abiding Americans having the right to bear arms without intrusion, so long as those arms aren't used to commit a crime - I get it. But, currently we have a system that "identifies" people more or less based on their race, religion, social or economic status. That's why this guy didn't pop up on the radar.
While it's true the most desperate of a culture may also be the most likely to turn to crime to get by, it's still wrong to profile. And it doesn't really work. I'm not going on a rant here, I have an actual point . . . somewhere . . .
Cal, you had asked earlier how could we have prevented this? The guy had money. He bought his weapons legally and with a background check etc. I would first propose that we make it illegal to legally purchase the items that make a semi-automatic fully automatic. That's simple. Would it stop people from getting the gear? No. But it makes it harder. Secondly I would propose that an individual OR FAMILY can only own X amount of semi-automatic firearms.
Would this solve it? Nope. But it would be a start. Hell, I'm a pretty damn good shot with a pistol or a rifle. And I don't own a firearm simply because I'm rational enough to realize that I might use it in the wrong instance and hurt or kill someone who didn't deserve it, even though I've been trained in the use of firearms since I was a kid.
I don't mean any disrespect to anyone who has contributed to this conversation, or anyone who owns firearms, it's one that is important. It seems a shame these only come up when there is a tragedy though. I hope those that had friends or family at the festival are OK. I know my friends were - cuz they blew it off (crazy gambling time!) but I hope yours made it home safe. To those that didn't - it's a g***amned shame and I hope your families can get past it.
Special thanks to those that know ground-work medic service. I think they saved a lot of folks.