it's rough being a loner these days, and every psychologist starts with that in the profile of the killer. i have heard social authorities actually telling people to be on the lookout for loners. the loner is the contemporary version of what previous cultures referred to as the 'barbarian' or 'savage': people not quite completely subject to our relentless socialization and picture of what it means to be human (=like us). direction of causation as well as extreme vagueness are problems with this analysis. are we loners weird wacky killer-people because we don't belong to the kiwanis, or do we avoid the kiwanis and they us because we're weird wacky killer people? anyway, i just want to alert you to the fact that even more elaborate efforts to socialize us loners or require us to party with you chumps is likely to have a reverse effect; you're becoming ever-more relentlessly though only semi-seriously caring, obnoxious, and indistinguishable from each other, and we tend to react badly.
in terms of beefed-up background checks, you might want to give a questionnaire: when was the last time you ate out? you don't sit in a study alone writing books (manifestoes, epic suicide notes, etc), do you? anyway, i just hope that the next mass killer is like a preppy frat boy with a thousand beer-soaked friends or a junior leaguer from dallas or a gay trelevision chef.