I feel that some posters in last couple of pages have been conflating the reasons and contributing causes of mass killings with the reasons and contributing causes of murder in the U.S. I think those are very different things, and their solutions only partially overlap. Mass killings: protect known targets (within reason), provide better mental health screening and care, decrease accessibility of non-hunting weapons. Murder: decrease accessibility of non-hunting weapons, increase conflict resolution training (?), increase opportunities and buy-in among the poor so that gangs and crime are a sub-optimal lifestyle instead of a dangerous but socially normal choice, take domestic violence seriously. I'm sure there are other routes and perhaps some problems with my suggestions, but I do think the problems are not identical.