We have laws on the books.
The shooter posted firearm images to a stranger on Instagram (I thing) and she wanted to know why. She saw it as a threat against her.
If you threaten someone with murder that is a felony, especially if you have the weapons to do so. That would have ended it had it been reported.
Not blaming the person he was messaging, just that it could have turned out differently.
Bears repeating:
We have laws on the books