Exclusive evidence shows protester was chased and then detained by police before disappearance

Nika Shahkarami has become one of the most known faces in Iran after she went missing on September 20 after attending protests in Tehran. Iranian authorities claimed she fell from a building later that night in an incident unconnected to the protests. But by analyzing over 50 videos obtained by CNN and speaking to six eyewitnesses, CNN has exclusive evidence that Nika was chased and then detained by police just a few hours before she went missing. CNN'S Katie Polglase reports.