In case you can't see, the boy in the red shirt has a very big knife in his hand.
Care: Pictures of the 4 dead stabbed people: http://imgur.com/a/dk5wo They dead people were killed by the boy in the red shirt.
I find I'm really fascinated by the group dynamics in this video. Like watching a heard of buffalow defend against a predator. Even the screams match what I'd expect to hear in nature. It feels like watching a national geographic video. My commendation to the men with the unbrellas.
It's hard to say without knowing much about who the assailant is. Mass murderers nearly always have psychological problems. They are often psychotic, suffering from severe depression, or in the midst of a mental breakdown. The assailant appears to be calm about the situation. I would guess he has either lost his mind, or he reached a breaking point and has turned his back on life.
At a guess I would say he was forced to endure years of monotonous lessons at the "Earth university", then was hired by a web developer who forced him to do all the public negotiations while the boss just sat around stoned? ...
Its a wonder he didnt kill more people.
My question is; why is he the only one with a knife? Don't people in Japan (i assume it's japan) carry weapons? How does the common man expect to defend himself against a knife wielding maniac? I suppose it doesn't occur to 'right thinking' people that something like that could happen, or that they would ever be put in a position to defend their lives. The world needs victims too, I guess.