In my opinion, this is a team, that is studying the effectiveness of this style of attacks. It has the advantage of terrorizing the public and saving the attacker to attack again. This is far more efficient than the suicide bomber that kills himself along with his victims in a bombing.
I agree: RECON. See how the public reacts, how our police respond, what their methods are, how likely leaks occur to the media (and about what), whether or not the MILITARY would get involved. They have gained a wealth of info. to "improve" their tactics to use in other cities, etc.
I recall about 6 months ago, there was a thread about RECON OF FIRE DEPARTMENTS by M.E., and a memo went out to all Fire Departments in New York, NOT TO GIVE OUT any info about how they respond to emergencies, equipment used, etc. Did you see that thread, does anyone remember it?