One woman has spent decades battling to win compensation for victims of Unit 731, the Japanese army's notorious germ warfare division. Zhao Xu reports.

"The Japanese really did it!" Wang Xuan said, recalling her initial reaction when she discovered a crucial piece of evidence in a file at the National Archives and Records Administration in Washington in 2003.

Wang is one of China's leading researchers into Japan's use of biological weapons during World War II. The file she came across contained the testimony of Tomosada Masuda, a former colonel in the Japanese Medical Corps and head of the 2nd Section of Unit 731, the Japanese Imperial Army's notorious biological and chemical warfare research and development unit.