On a day when Chennai's hold on a massive, peaceful protest loosened suddenly, the videos tumbled out in quick succession - men and women in police uniforms setting autorickshaws on fire, vandalising property, raising their lathis or batons high above their heads and bringing them down with crashing force on parked vehicles. Within minutes, the videos had been tweeted by top Tamil personalities like Kamal Haasan and Arvind Swami, demanding the police explain what was caught on camera. Four days after the violence, top police officer V Balakrishnan said that an investigation should be completed within a week to determine if those in uniform were really police personnel, and if so, to identify them. He also acknowledged it was a mistake for his force to have ignored what was spreading quickly on Facebook, WhatsApp and Twitter. "One lesson for us is to track the social media, particularly messages going viral and take cognizance," he said, acknowledging that an official comment on the videos should have been shared much sooner.