A documentary game titled Eyewitness appears to let you play as a photographer in the setting of the Nanjing massacre period during the Japanese invasion of the city. Unfortunately apart from very few information online, the game does not seem to be available anymore.
Harris Wai, from Hong Kong Polytechnic University’s Multimedia Innovation Centre, has developed this game about Japanese war crimes (thanks Espen). You play the role of a photographer who needs to document the Nanjing Massacre.
Links to the game appear to be not working, but according to this site http://highla.altervista.org/storia.htm (Italian only) the game was presented in 2003 to the Games Developers Conference in San José.