So what? The racist right-winger who massacred a church-full of blacks was allowed to buy a gun because of the insane laws foisted on us by the nra and its lapdogs. The right-wing nutter, Houser, had an arsenal of weapons he was able to buy under our current gun laws. The list goes on and on.
People who support the insanity of our current gun laws are morally responsible for all of the gun killings that are perpetrated by these extremists.
If someone wanted to kill a church full of black people that badly, they would just decided to blow it up or gone on a murder spree with a knife, or throwing stars, etc if they couldn't purchase a gun. Having tougher gun laws will not prevent deaths from crazy people. Period.
The difference is that you can kill way more and way faster with a firegun. Throwing stars would be deadly very seldom and you need to be very skilled with a knive to kill many.
I personally think tougher gunlaws will prevent a lot of these invidents... but only not all. See germany. We have no allowed guns so far that everyone can buy but we have sports with guns. The result is that there are many weapons in private homes. And these weapons were used, often enough in school killings too. Often childs of parents doing it for sport.