I love the talk of these magical law-abiding citizens who don't abuse guns.
Guy goes crazy, catches wife in bed with another guy, loses his mind, picks up the gun in his garage and shoots her. He used to be law abiding. (And btw, these cases aren't rare, I could cite a dozen just off the top of my head)
Stupid teenager and his 3 buddies go to a 7-11, they're horsing around, decide to be dumb and steal a 6-pack of beer, it goes wrong, one of them happens to have a gun, shoots the cashier. No previous history of criminality, no previous convictions, hey, maybe it was his buddy's gun - he just happened to be holding it.
9 year old boy finds one of his father's guns in the basement, plays around with it, accidentally shoots his sister and the family dog. No history of criminal behaviour.
Guy owns house backing onto ravine, hates how neighbourhood cats and dogs wander on to his property. Sees a beagle taking a dump, picks up his gun to teach it a lesson and misses, shooting the mother of 3 who happened to be walking the dog. No history of criminal behaviour.
Guy's business is crumbling, he's got debt collectors showing up, he's under stress, they're relentless, he orders them out of his store, they refuse, he picks up a gun and shoots. No history of criminal behaviour.
Guy's wife tells him she's leaving him and the kids and is going to clean him out and by the way, his dick is small and she's repulsed by looking at him. He's enraged, picks up his hunting rifle, shoots her, the inlaws who live on the main floor of their house and then takes his own life.
Everyone is law abiding initially.