Powch was put behind bars for three counts of sexual assault, for which he was jailed in 2004 for nine years, four months.
Justice Health, which caters to prisoners' medical needs and is controlled by NSW Health, refused to comment on Powch's case.
Powch, a hardened criminal who has been behind bars most of his adult life, is in jail until October 19, 2013.
In the 1970s, Powch was involved in armed hold-ups with Ivan Milat, who was cleared of the charges but went on to become a serial killer.
, 44, and Ross, 38, were originally accused of attempted murder but pleaded guilty to a lesser charge of assaulting and injury at Edinburgh Sheriff Court last month.