“Flash mobs” began as a relatively harmless Internet phenomenon in which groups of people would meet at a set location and time advertised on social networking sites. More recently, however, in Philadelphia, Chicago, Washington and elsewhere, the mobs have led to attacks, thefts and other crimes, and law enforcement agencies are looking for ways to address the new criminal trend.

For the past couple of years, groups of young people used texts and social media messages to organize incidents in which they intimidated shoppers and residents in Philadelphia's Center City area. In the latest incident on July 29, the mob assaulted bystanders. In early August, city officials responded by implementing new law enforcement policies, including an earlier curfew for minors in some parts of the city, increased police presence in those areas and stricter penalties for parents of teens who repeatedly violate the curfew. Mayor Michael Nutter signed an executive order to temporarily begin the curfew at 9 p.m. on Fridays and Saturdays for all minors under age 18 in targeted enforcement districts where most of the flash mobs had occurred. There have been no criminal flash mobs in Philadelphia since early August, and the special curfew remains in place pending action by the city council on a proposal to update the city's curfew law, says Nutter's Press Secretary Mark McDonald.

Flash mobs are “high on the radar screen of law enforcement,” says Nancy Kolb, senior program manager for the Alexandria, Va.-based International Association of Chiefs of Police (IACP) Center for Social Media. Police are using software that looks for certain keywords and terms that could indicate a flash mob event that is coming up, Kolb says. Also, law enforcement can use social media records to identify participants in flash mobs.

Social media may pose some challenges for law enforcement, but it also has helped to solve a lot of crimes, Kolb says. “Whether it's identifying [suspects] from videos that are posted on a social media site, or frankly, people posting themselves on social media sites owning up to criminal activity or behavior that they've been engaged in,” she says.

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