Twenty years ago, the Chinese military gunned down student protesters in Tiananmen Square. As twentieth anniversary events are held around the world, we speak with Wang Juntao, a prominent Chinese dissident who was sentenced to thirteen years imprisonment and now lives in exile in the United States, and Philip Cunningham, an American journalist who marched with the students and is author of a new book Tiananmen Moon: Inside the Chinese Student Uprising of 1989. [includes rush transcript]