It seems likely that at the time he didn't have such a record, and was perhaps reduced in rank for similar offences? To be reduced from WO to Pte it must have been a Courts Martial - is there anywhere where the results of these are available on line?
Personally...it makes me sick! How someone of this nature managed to get into the position he was is beyond belief!! Somebody must have come across him in his career and thought he was a bit of a deviant.As for demoting him...that's too good...have fun in prison!!