Nutters with guns and motive, mostly in the US. If the solution were simple it would have been done.
I don't think it's anything to do with publicity; folk with this intent are really unaware of anything outside their own immediacy.
And I don't think removing, revising or reinterpreting the 2nd amendment is going to happen in the near or distant future. The Amendment was instigated so that people could protect themselves in dangerous times - hardly relevant today (mostly)
But there are things that could be done to reduce the frequency of these hideous events, not just in the US. And, yes, I know some of these are a little trite:
- understanding extreme mental conditions; making it Ok to admit to them, discuss them etc with professionals - before they get that bad. Talking reduces problems.
- given that owning guns will remain legal: in Federal law, remove all but simple hunting guns from sale or possession; compensate hand-ins; provide severe restrictions on storage and access; make vast increases in penalties for offences. Prosecute organisations that flaunt these new laws. This doesn't have to be done in a single step, but it would help