Twenty-five years ago, Wang Nan took his camera and headed out to Beijing's Tiananmen Square, where tens of thousands of people had gathered calling for democratic reforms. The 19-year-old told a friend he wanted to record history.

Before he left his home late on June 3, 1989, he asked his mother: "Do you think the troops would open fire?" She said she did not. Around three hours later, he was shot dead by soldiers.

As his 77-year-old mother, Zhang Xianling, prepares to mark the 25th anniversary of her son's death, she is under around-the-clock surveillance by eight police and security officers.