she's been talking to eyewitnesses like keivan, a medical student. treat wounded protesters, and has since fled iran. >> (speaking farsi): >> narrator: keivan says he was arrested for helping the protesters and taken to a secret detention center. his account of what happened next is horrific. >> (speaking farsi): >> (speaking farsi): >> (speaking farsi): ♪ ♪ >> narrator: iran has denied abusing prisoners, but keivan's account echoes the testimony of many other detainees. since the beginning of the uprising, thousands of protesters have been arrested and locked up in regime black sites or police stations, like the one in this video from the city of karaj, posted online in september. >> narrator: zar is taking the testimon of a man who is still inside iran and asked for his identity to be concealed. he says he was held in a black site in the northwest of of the country after being arrested at a protest in october. >> (speaking farsi): >> (sniffles) >> narrator: in november, the crackdown escalated. >> (speaking farsi): (audience responding) >> narrator