"The Truth" huh? Hold it there buddy... that isn't a phrase to throw around when talking about any form of "media."
This movie, which I will clearly say I have not seen but do intend to see, comes from one side of the argument mostly favoring the Chinese side but includes documents and research supported by the United States as well.
With that said, I will say that I have been to China, seen the Chinese view of the massacre and read documents (translated) and spoken with professors. I've also seen the denials from the Japanese side. The Chinese side is a hell of a lot closer to what seems to be the "Truth" I'd say, but don't ever assume that a movie is "truth." Especially when I believe the movie is based around fictional characters used to present the massacre from different aspects.