Did Police Stand Down During Riots in Philadelphia?

The Philadelphia Eagles won the Super Bowl, and hundreds of fans rioted, tearing up the city and destroying property. [When you look at these videos of violence and looting, you cannot help wondering what the police were doing during this time. Is violence now tolerated in order to further condition law-abiding citizens that martial law is necessary? Please let us know if there is an explanation from police for not preventing this. That's what they are paid to do.] [...]