Experts who devote themselves to protecting history and investigating the crimes in the World War II speak at a mourning activity to pay tribute to the victims in the Nanjing Massacre 78 years ago at the Chinese Culture Center of San Francisco in California, the United States, Dec. 12, 2015. More than 300 people attended an activity held in the Chinese Culture Center of San Francisco on Sunday to mark the death of victims in Nanjing Massacre from Dec. 13, 1937 to January 1938. (Xinhua/Liu Yilin)
