"People compared online gang violence to cyberbullying, but it felt different," he told me. "If [a gang member] makes a comment online, it can quickly become homicide. People are rarely killed over cyberbullying."

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Tweeting a location, like Barnes did just before her death, might provide an opportunity for violence. Referencing physical locations on Twitter offered both the opportunity for volatile situations to bubble over by drawing rivals to a mutual location and a warning for rivals to stay away.

"Young rappers are getting involved in Twitter battles and tweeting their location and then they are killed in those locations," Patton said. "And it happens fast."

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Likewise, among gang-involved youth on Twitter, firing off an angry, violent or mournful tweet seemed to trigger violent reactions—the same principle that fuels harassment by online mobs. But in this case, the study found, online aggression could easily spill into real world violence.

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One of the most interesting things about the role Twitter plays in gang violence is that it creates a place where it all just unfolds in the open. Patton hopes that might create opportunities for outsiders to intervene and help stop it—and also, then, for police to monitor it.

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"What we know is that a lot of people are having conversations online that lead to people harming each other," he said. "This is an emerging issue and the problem is only going to grow."