Identifying potential shooter is not actually the problem. It's how you do so..and what do you do when you think you have a live one. By what law can you detain someone that fits a profile? Disarm them? Surveil them? How far do you go to 'get it right' when getting it wrong has such severe consequences? What of the innocent? We all are..before we act, right?
Does any American want to hear some possible answers to the gun problem, unless they have suffered a personal loss that causes them to show concern?
I think we're agreed somewhat on how to identify potential mass shooters, to some degree at least. You've taken that to a different level that shouldn't be just ignored.
Of the 5 identifying characteristics of a potentail killer that I've named, they're not the only ones the police could consider. They are only 5 possibilities for the police to start paying attention and that's ot an infringement on any gun owners' rights.
The peaceful and lawabiding gun owner will almost certainly practice shooting of a nature that would enhance his ability to accomplish that which he intends to do with his guns. It's not likely that he will hide his activity and so there's no reason why the police can't pay his home a visit in order to determine whether he intends on staying peaceful.
There will be at least some indications available to the police that could and should allow an arrest.
Do any Americans really want to understand?
It could be your wife and children that the good guy next door kills with his gun. You've already made yourself into a more likely target than other Americans who are 'completely' sympathetic to unrestrained guns and their uses.
And me too fwiw, even though I'm on much safer ground.