Posting number 4 links to a story about an "army" of two, and one of them was an FBI agent.
If one man and possibly an accomplice can cause that much havoc (remember Norway??)... just imagine if they spread out over a good sized city and co-ordinated bombings, hostage situations, standoffs...
someone could probably pull off some big bank robberies in the interim too
Man am I so ever glad that street gangs are usually too stupid to try that kind of stuff