Last Monday night, while Baltimore residents set fires and looted stores to protest the death of 25-year-old Freddie Gray, Mayor Stephanie Rawlings-Blake announced that police would use social media video and images to prosecute rioters. "We will be holding people accountable," she said.
More than 200 arrests related to the rioting have been made since then, and about half of those arrested have been released without charge. Several videos of the violence and looting made their way to social media, but there's no indication that posts have directly resulted in charges. Whether or not Baltimore authorities decide to actively pursue offenders depicted on social media could come down to how much pressure the community puts forth for arrests. Or how much help the police get from members of the public to identify offenders. 
When rioters took to the streets in Vancouver after the 2011 Stanley Cup Finals—resulting in fires, stabbings, and 139 hospitalizations—authorities used more than 5,000 hours of social media video footage to file charges against as many as 300 people. There was, according to a 2011 Department of Justice report, "high public interest in seeking out the identity of the rioters," and local police received more than 3,500 tips to help identify offenders.
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