The 1-hour demonstration Sunday night caught police off guard, and the protesters had dispersed by the time officers arrived, the Oakland Tribune reported Tuesday.
Extra officers had been brought in for rallies Friday and Saturday nights, but patrol levels were at normal numbers Sunday night, said police spokeswoman Johnna Watson
An anti-war group with a history of peaceful marches had received permission to hold a rally to mark the 11th anniversary of the start of the U.S. war in Afghanistan. However, another, unnamed group posted on Facebook it was holding an anti-imperialist event at the same time and the police department was caught unaware.
Police said the protesters gathered about 6 p.m. at Frank H. Ogawa Plaza in front of City Hall. About 7:15 p.m. they walked north several blocks before coming back to City Hall.
During the march, police say, glass front doors and windows were broken at two city offices and about nine businesses. Tires were slashed and windows broken on two cars.
About $12,000 in damage was one to public property and several thousand dollars more to private property.