I have never ever found any documented reports of an apology from the US for covertly pardoning and allying with Unit 731. In fact, I read they outright ignored victim pleas as communist blabber and that was it from them. Even today neighboring Asian countries will constantly remind Japan of Unit 731 but the US has nothing to say of their involvement.
There's also nothing about what they gained from their research. All it says is it was a strategic move to intercept communism and that was it. What does this even mean or what are the details here? The mastermind behind Unit 731 and his cronies the US got ahold of went on to live full and ordinary lives unscathed.
Needless to say, that's the equivalent of letting Josef Mengele get off the hook. So I'm wondering what was gained or so important that America decided to not even attempt a "you have outlived your usefulness" after it was all said and done.