I asked his nephew this question back in 2011. The explanation I got was Granger had just returned from the UK as a young officer and was not a decision-maker. Any such decisions were made way over his head. He never admitted nor denied his uncle took part in any action, he was just not a decision-maker.
It’s like a 45 year old adult putting a gun in the hands of a 25 year old then ordering him to shoot someone in the back on 5th Ave (like Trump). If he does, he actually didn’t because he was ordered by the 45 year old.
So he has been adjudicated as innocent because he did but he also didn’t!