At least four times in the last year, Philadelphia has been taken over by flash mobs made up of massive numbers of teenagers who congregate in one place at the same time. The gatherings are usually coordinated through text messaging, Twitter, or other electronic means. It sounds innocent, (and indeed, most flash mobs are utterly benign) but lately, the gatherings in Philadelphia have taken a violent turn, resulting in injuries and damage to properties and businesses.
We speak with Philadelphia's Deputy Police Commissioner Kevin Bethel about how the city is addressing this problem. And New York Times National correspondent Ian Urbina explains the origin of flash mobs and how they came to be.
Read Ian Urbina's article in the Times, "Mobs Are Born as Word Grows by Text Message."
Below, a more typical flash mob: quirky, upbeat, and decidedly non-violent.