Here is an idea that has been kicking around my head for a wee while, ever since I bought my brother-in-law a drone for his birthday.
It must be possible to have a taser carrying drone. Such a device could easily sit in a box above key security cameras in places like shopping malls and airports etc.
When suspected trouble is spotted, the drone could be instantly launched and be close to the action in seconds. The onboard camera can confirm for the operator if this is a serious event, e.g. someone trying to stab people or shoot them. If they are then the taser could be fired, hopefully leading to immobilisation of the perpetrator long enough to be apprehended.
Such a system might not only minimise the harm done by a perpetrator by getting there in seconds but also greatly reduce the risk of harm to those who have to apprehend him/her.
It wouldn’t cost that much either. Probably would require legislation though.
It wouldn’t do much good in the case of a suicide bomber or a vehicle weapon but a lot of these random nutter type events in schools, malls etc seem to be lone individuals on foot with knives or guns.