escalated and happened not far from where president obama and more than 50 world leaders were juggling issues facing afghanistan and nato. the city s top police officer blames a small group of troublemakers. if there was a group of what we commonly refer to as the black bloc folks who kind of rallied together, they put their masks on and found out from the crowd they would charge the stage and try to break through and assault our cops. that exactly what happened. they rallied, charged the cops and assaulted the officers. we responded, so far today we re up to 45 arrests today. and tonight cnn s paul vercammen is live down there in the crowd or where the crowd was earlier. what happened out there? who did what to trigger the mess? reporter: when you re looking at it from the inside out it s difficult to determine if there was one flash point as the superintendent said, he believed that the black bloc protesters were going to charge the stage, that s when it became clear