The Japanese had entire city-sized lab complexes in China devoted to "studies" in bio-war.
Bigger - and as brutal - as anything the Nazis ever did.
So why don't you know about it?
Missing from this film is a dirty secret.
The US government was so interested in the "data" that the Japanese generated and in the advantages they thought it would give them that they chose not to prosecute the Japanese involved to keep a lid on the story and the data.
The winners write the history and in this case the winners thought there was an advantage to writing this part of the story out.