I do not know much details about Unit 731. However, I CAN tell you about my own personal encounter (of a sort) with that notorious WWII organization.
About 30 years ago, when I was a young journalist working at an English-language daily in Tokyo, I was assigned to do a story on the death penalty in Japan (this is an interesting topic, about which I have talked elsewhere, first of all, that it even still exists in Japan, whereas most Western countries (in Europe particularly) have stopped).
In preparation for this assignment, I went to talk to an old Japan-native reporter in the office (as in REALLY old, he should have been retired years before, he was nearly blind, and mostly kept to himself). He began to tell me a story of the man who had been on death row the longest, for a crime committed in 1947 during the chaotic postwar period.
As he continued, I realized that I KNEW this story. When I was younger I had read an entertaining book (can’t remember the title now) about famously notorious crimes in Japan. One chapter was about THIS one.
A man had robbed a bank. (For a bank, we usually think of spacious hall with pillars and tellers. Well, this was postwar Tokyo and the bank branch was a clapped-together building, like everything else in bombed out Tokyo was like.) When he entered, he told the staff and patrons that he was a representative of the Health Dept., that there was a flu epidemic going around (quite likely in this chaotic period) and that everybody there would need to drink this medicine he was carrying. All dutifully lined up to take a sip.
But it was deadly poison and all were dead within minutes. The man scooped up the cash and vanished.
So far, this I knew from the book, and that enterprising police detectives had within months tracked him down, arrested him, put him on trial, found guilty, and sentenced to death. Justice served?
Well, not quite.
The part that the book writer had NOT known, and which my informant told me, was that the man had been a member of Unit 731, and was using some of its byproducts to commit his crime.
So then, said my informant, the man went into limbo. Never executed, but never released back into society either. Why not? Because the man had apparently cooperated with the Occupation authorities (the Americans) telling all about Unit 731 for use by U.S. Intelligence, which then remained secret for decades thereafter. In exchange, he would not be punished for his WWII activities.
But then, he commits murder. So off he goes to prison. But they will never execute him, my informant said, because of the promise made.
None of this was public knowledge. It was NOT admitted policy, but everyone involved (including my reporter friend) knew this (but would never put it in writing).
Ah. Well. The most fascinating part of the story, and I did not put any of this into my death row opus. (I did not even bother, as I knew it would never have passed upper management…)
A few years later (I was back in the States by then), I read that this man, longest-serving death row inmate ever, had passed away in his cell at around the age of 95.
Probably the last surviving member of Unit 731.