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Paul Sakuma, Associated Press
A sign is shown in front of broken glass at Tully's Coffee shop in downtown Oakland, Calif., Thursday, Nov. 3, 2011 after a Occupy Wall Street protest earlier. Cleanup work is under way at Oakland's city hall plaza the morning after a massive anti-Wall Street protest turned violent and chaotic. Graffiti is covering a number of businesses in the immediate area around Frank Ogawa Plaza, where thousands had gathered for a mostly peaceful protest Wednesday. Some windows also are broken, and debris is littering the street.

OAKLAND, Calif. — Dozens of people who participated in a massive anti-Wall Street demonstration returned Thursday to help clean up after a night of violence by what they characterized as a rogue band of troublemakers.

Oakland officials were still assessing damage to properties surrounding the City Hall plaza, where an estimated 7,000 people had gathered a day earlier to protest large corporations and banks that they blame for the economic downturn.

About two dozen businesses — mostly chain stores, such as Burger King and Tully's Coffee — were seen with shattered glass, spray paint and other damage to their storefronts. Officials said 18 windows were broken on buildings, including City Hall and a police recruiting center.

On Thursday morning, the site of what had been energized, carnival-like rally attended by families, students and labor union members looked battered and beleaguered, with trash and vandalism debris strewn everywhere. The city, however, went about its business, with workers clearing the streets and most businesses reopening.

City Administrator Deanna Santana said she was "saddened by the vandalism that occurred by a small group of isolated individuals."

"We obviously know that Oakland needs strong businesses, and I want to personally apologize for what has occurred," Santana said.

Interim Oakland Police Chief Howard Jordan said three officers were injured during the demonstration. The most serious injury was an officer bitten by a vandal.

"Generally, we consider them anarchists and provocateurs, people who are intent on causing damage even when things are peaceful," Jordan said of the troublemakers.

"We are planning on having a strong presence again today," Jordan said, adding that he was unaware of any planned events that merited crowd control.

Quick to disavow the violence that threatened to hurt their cause, protesters pitched in with the cleanup effort, sweeping up debris and scrubbing off graffiti.

Two men who were staying at the Occupy Oakland encampment on the plaza spent their afternoon scouring black paint from the side of a building near City Hall.

Shari Rivers, 32, the manager of a Tully's Coffee on the plaza, was sweeping up Thursday after protesters broke windows, stole some property and knocked over the cash register overnight.

"I cried," Rivers said. "It's very disheartening. I am part of the 99 percent and have supported this movement. My feelings were so hurt."

Jordan said officers arrested more than 80 people in the late-night skirmishes.