Temple University in Philadelphia is on edge after seething “flash mobs” of violent teens roved the campus Friday night, terrorizing and randomly assaulting students. Four teenagers ages 14-17 have since been arrested and police presence reinforced around the rattled campus.

According to a statement from Temple security, hundreds of juveniles gathered along Broad Street around 8.30pm on Friday and roved the campus for nearly two hours, in what quickly devolved into an uncontrollable night of horrifying violence. Over the course of the evening two police officers were assaulted , six students injured, and one robbed. A police horse was also punched in the face.

The group of roughly 150 students reportedly organized the “flash mobs” on the picture sharing platform Instagram. They had planned to meet at 8pm.

School officials issued an alert to warn Temple students about “large groups of juveniles along Broad Street on/near Main Campus.” But in many cases, the warning came too late.

Police said the violent mob went from street to street, picking Temple students at random, physically assaulting and mugging them.

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