i don't agree that this type of incident is unprecedented in the US. this just happens to be the worst in recent memory,but i can recall several,namely Laughlin nv or back in the 70's the july 4th massacre of 5 OMC by the HA's in Charlotte. but i do think it's possible that this was provoked by law enforcement,since some undercover agents,or informants are sometimes behind these violent flare-ups.