Well, because the law states that felons can't own guns. I won't say whether I agree with it, but it answers your question.
But how can that be, if gun ownership is a God-Given right? We don't remove any other "right" from convicted felons. Unless gun ownership isn't a "right".
The problem is how we define "felony." Not all felons are violent, not all are drug addicted, not all are pedophiles. I mean, someone who writes a bad check loses their gun rights? That's nuts. I don't have problems with violent felons losing gun rights. But non-violent ones, no. To me, that's not right. What makes something a felony has nothing to do with its level of violence or even if there is a victim or not. It's simply defined as a crime where you can be sentenced to jail for more than 1 calendar year. If you can be sentenced to 366 days in jail for that crime, it's a felony.
I kind of see where you are coming from here. But I take the other side.
Every time there is a mass shooting, we find out two things.
1) Everyone in that person's life knew he was a nut.
2) he had no problem getting a gun, usually within days of the incident.
So if you had a background check on your hypothetical teen prankster who now has a good job and was a solid citizen, most people wouldn't have a problem with him having a gun.
Conversely, if someone did even a modicum of investigating Joker Holmes, Audrey Hale, Sueng-he Cho, and Devin Kelly, they'd have found them bad candidates to own guns.
Which is why I do the comparison to my mortgage/Job Search/sponsoring my wife. They actually- you know- looked into that stuff. So they know I'm not going to be a bad employee, or default on my mortgage, or do a green card wedding for a Chinese spy.
A teen prankster who calls in a threat to a school, where they know who it is and that he's screwing around being stupid, felony. Loses gun rights for the rest of his life. I mean, that's nuts. My dad said his friends brought their deer rifles to school on Friday and left them in their trucks because after school they were going straight to the woods. Even had their camo on the seat of their truck, too. Nobody was charged with any crimes for that, but now, it's a felony.
And the reason they don't allow that anymore is someone at some point took one of those deer rifles into a school and started shooting people.
When you criminalize everything, you make criminals out of everyone.
Nuts, isn't it?
Perhaps. I am all for Criminal justice reform and expunging people's records after a certain period of time.
But it's still too easy to get a gun in this society.
Going back to our topic of the thread, I wouldn't be surprised to find this shooter had some kind of mental breakdown.