If I understand correctly, you're saying the police attacked protesters who were guilty of vandalizing property. If so, you're absolutely wrong. In fact, the police IGNORED the tiny handful of protesters who engaged in vandalism. In fact, I was on the scene shortly after the vandalism occurred. I remember seeing the broken glass, and I recall people expressing surprise that the police did nothing to intervene.
Then the police suddenly went berserk and began attacking everything in sight. They assaulted holiday shoppers and reporters. There was a famous incident where they asked a woman driving a car to roll down her window, then maced her. They invaded Capitol Hill, which had nothing to do with the WTO protest.
There were an estimated 50,000 people on the streets during the WTO protest. I doubt that more than a few dozen - well under 1% - were vandals. Some people have speculated that the "anarchists" who
committed most of the vandalism were actually operatives PRETENDING to be anarchists in an attempt to give the protesters a bad name. That would explain why the police just stood by and watched while they did their dirty work.