As was the case with Occupy Portland, the mob at Zuccotii park is apparently hoarding items which could be weaponized at a moments notice:
"....people who have a known history of violent interaction with the police” have been gathering in the park, and “makeshift items” that he said could be used as weapons, "such as cardboard tubes with metal pipes inside, had been observed among the occupiers' possessions." He also noted that after the October 1st Brooklyn Bridge march, "knives, mace and hypodermic needles were observed discarded on the roadway."
-----source : http://gothamist.com/2011/11/15/city_claims_occupy_wall_street_prot.php
