From NY Times: what happened on the Brooklyn Bridge

There were no physical barriers, though, and at one point, the marchers began walking up the roadway with the police commanders in front of them – seeming, from a distance, as if they were leading the way. The Chief of Department Joseph J. Esposito, and a horde of other white-shirted commanders, was among them.

Ozier Muhammad/The New York TimesPolice secured some protesters’ hands with plastic ties.

After allowing the protesters to walk about a third of the way to Brooklyn, the police then cut the marchers off and surrounded them with orange nets on both sides, trapping hundreds of people, said Mr. Dunn. As protesters at times chanted “white shirts, white shirts,” officers began making arrests, at one point plunging briefly into the crowd to grab a man.
Charges against those arrested were not immediately available. A freelance reporter for The Times, Natasha Lennard, was among those arrested.
Mr. Dunn said he was concerned that those in the back of the column who might not have heard the warnings “would have had no idea that it was not okay to walk on the roadway of the bridge.” Mr. Browne said that individuals that were in the rear of the crowd that may not have heard the warnings were not arrested and were free to leave.
Earlier in the afternoon, as many as 10 Department of Correction buses, big enough to hold 20 prisoners apiece, had been dispatched from Rikers Island in what one law enforcement official said was “a planned move on the protesters.”
Etan Ben-Ami, 56, a psychotherapist from Brooklyn who was up on the walkway, said that the police seemed to make a conscious decision to allow the protesters to claim the road. “They weren’t pushed back,” he said. “It seemed that they moved at the same time.”
Mr. Ben-Ami said he left the walkway and joined the crowd on the road. “It seemed completely permitted,” he said. “There wasn’t a single policeman saying ‘don’t do this’.”
He added: “We thought they were escorting us because they wanted us to be safe.” He left the bridge when he saw officers unrolling the nets as they prepared to make arrests. Many other who had been on the roadway were allowed to walk back down to Manhattan.
Mr. Browne said that the police did not trick the protesters into going onto the bridge.
“This was not a trap,” he said. “They were warned not to proceed.”

Full Story Here:  http://cityroom.blogs.nytimes.com/2011/10/01/police-arresting-protesters-on-brooklyn-bridge/?pagemode=print