in her first interview. >> why did you want to do this? >> it's just an important time to speak up. >> reporter: powerful new d i details with a warning. at times they can get graphic. >> i know it's hard to tell this story. >> yes. >> it's hard, gianna, for you to hear this. >> reporter: and a powerful confrontation with bill cosby himself. >> i was yelling and saying to him, "you're sick." >> reporter: one woman, standing for them all. >> shero, joan of arc. >> she took us from victim to survivor. >> i just needed to make the first step.ooiv after that, it was in god's hands. hello. and welcome to "dateline." for years andrea constand