You need to understand that stricter gun laws doesn't mean this guy wouldn't have his gun. Stricture gun laws means a person shouldn't have weapons past a certain level, and should pass a mental and physical evaluation before being allowed to buy a gun, as well as not being able to buy guns when you're under severe investigation.
Realistically, none of these things if implemented would have stopped this guy from having his gun at that moment, so this doesn't actually defeat the argument of stricter gun laws.
The black market of ghost guns are on the rise ,if you have skills in drill pressing or milling your able to make firearms. They've even made milling machines for creating firearms which isn't illegal even so you can claim it to be for other use or purposes, 3D printers is also an option but it's expensive well for now atleast.
Philippines has strict gun control look these guys are creating ghost guns with no problem, also the full documentary showed how these guns made it all the way to the United States,Mexico, and South America.
[video=youtube;1_ZRk0A4QYQ]https://www.youtube.com/watch?v=1_ZRk0A4QYQ[/video]
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Most firearms that are being purchased are ghost guns that can't be linked, specially made so they can't be traced or even known to existence under federal radar. The government can start claiming anyone to being whatever they what them to be under their jurisdiction.