The O’Farrell Government did not oppose Williamson’s release, which was announced by a parole board this morning.

Opposition leader John Roberston said there was ‘‘simply no excuse’’ for the government’s inaction.

‘‘While the victims of these horrific crimes fought against this criminal's release, the Attorney General Greg Smith apparently didn’t deem it worthy of his attention,’’ he said.

Mr Robertson said the Attorney General had also failed to consider using extra powers to keep serious sex offenders behind bars or supervised in the community.

‘‘Under the Serious Sex Offenders legislation, the Attorney General can apply to the Supreme Court for a ‘Continuing Detention Order’ or an ‘Extended Supervision Order’ against a sex offender whose sentence is about to expire,’’ he said.

A spokesman for Mr Smith told AAP the government had acted on the advice of Corrective Services Commissioner Rod Woodham.

‘‘Commissioner Woodham advised there was no case for the state to oppose parole,’’ the spokesman said.

‘‘We accepted that recommendation. We note this serious offender will be subject to strict conditions.’’