Mass shooters are Kamikazis dive bombing our own Ship of State, America. Don't buy the "family ignorance" excuse of their parents! They shoulda known! Too many guns make impossible direct control. Corrupted political protection of gun sellers disguises needed legal change. Conservatives hold the family high as a source of values. So motivate, among church goers, a groundswell to legislate into liability law, a "Brother's Keeper" base. Co-dwellers are the largest, closest link. Make "Brother's Keeper" law so draconian that it will force parents and other co-dwellers into their "brother's" bedrooms, etc. to gain responsible custody of parabellum semiautomatic black rifles and Glocks.
"Mass killing guns in your home? Your castle will be sold for victim compensation." Give police adequate budgets to search and seize these exceptional black parabellums based on "Red Flag" warnings. Black guns are purchasable predictors, although imperfect, of murder and mayhem to come. Let the liability law say, "Get co-dweller's guns safely stored, or inform Police. They are used for mass shootings. Civil society will apprehend their users. But it will also take away all your valued property." A few publicized horrible examples of spoilation might help.
