It's been a tumultuous few weeks in China, with the death in custody of the country's most famous dissident Liu Xiaobo shot to worldwide fame when he won the Nobel Peace Prize in 2010, an award he could never collect. He was already serving 11 years in jail, convicted of trying to overthrow the state and he died a few weeks ago from cancer, under guard in hospital. Our China correspondent Bill Birtles spoke to Jonathan Kamm - an American businessman who has spent almost three decades presenting prisoner lists to China's Government, in the hope of highlighting specific cases. He said he regularly raised Liu Xiaobo's plight.