FWIW, in an Aikido Journal interview Gozo Shioda states: "Ueshiba Sensei was implicated as a war criminal and accused of class G war crimes. His foundation [the Kobukai] was taken away and his activities were stopped."
As I said, I am unaware of O-sensei being convicted of any war crime but perhaps he was implicated. An implication wouldn't be too surprising considering his wartime activities and associations. The fact of a "non-conviction" would serve to imply that the Occupational Government, at least found that he played a less than nefarious roll.
Here is an associated thread: http://www.aikidojournal.com/forums/...ic.php?t=11543