It isn't new. Disturbing, but not new- this kind of behavior is the very origin of our term "amok", it's either Malaysian or Phillipeno (sp, I can never get this one right). The Japanese and Chinese have similiar, uhm, "traditions" (?). Basically, some guy (it's almost always male) flips out, and attacks a crowd, killing and injuring as many as he can until he killed or incapacitated.

I was reading a paper on it a couple years ago doing a paper on spontaneous violent outbursts, and IIRC part of the leading theory was that it was partially a stress reaction to a highly stratified and hierarchical social structure.