Delegates from Japan attend an international symposium on the war crime of Japanese Army Unit 731 in Harbin City, the seat of former headquarters of Unit 731, northeast China's Heilongjiang Province, Sept. 24, 2015. Unit 731 was a biological and chemical warfare research base established in 1935. At least 3,000 people died at the base between 1939 and 1945, mostly in experiments for the development of biological weapons. (Xinhua/Wang Song)
