I have this reaction every time some mentally ill person murders some people or sets fire to a building or something.

In general, people react with "The laws need to change! We need to ramp up surveillance/social care/police capability etc etc" or even the "What shall we do? Something needs to be done!" type response.

But I think that usually the answer is "Do nothing". It was just one edge-case disturbed individual. This is not a common event, and will not be a common event. We cannot generalize any learnings from this tragic event. We just keep on keeping on, and know that one time in a thousand a bad thing will happen but for the other 999 times everything is fine and will be worse with more rules and restrictions.