However law abiding people may have been, at the point where they turn those guns on other people they have ceased to be law abiding (leaving aside those cases of gun killings where legitimate self defence is involved, which I understand to be a relatively small fraction of gun killings).

I believe that in a high proportion of gun massacres the weapons used had been legally purchased. So is the case in those instances where children have used their parents' gun with tragic result.

How about strict laws that all lethal weapons should be securely stored in a gun cabinet, with room for specific exceptions to that to be permitted for adequate reason, Bruce?