Huh?? Generals are just as subject to normal criminal law as anyone else, especially once they have retired. This was not a official duty.
BTW: Please don't read this as saying I agree he should be prosecuted, but I don't understand your statement. Can you please provide a link or explanation for what you meant?
I don’t agree with what he did but everything a 4 star does is official. Also there are laws which protect senior officers and enlisted.