[lostalex]

There's no way to prevent this type of thing, sometimes people just snap. They just lose control.

Unless you have airport style security at every place where there are large groups of people there's nothing you can do. Every cinema, every grocery store, every mall, every post office, every school. It would be impossible.

It's just like cars. You just have to accept that there are going to be drunk drivers that kill people sometimes. You can make all the laws you like, but people are still gonna die sometimes.