Western Australia's worst sex offenders released from jail, AAP reports.

Known as "TJD" for legal reasons, the sexual sadist had a background of ghastly sexual assaults to women. These assaults were committed when he was just 15 years old, consisting of attacks on 13 women with the use of a weapon, even fake ones, to draw his victim into submission.

He was released from jail by a Supreme Court judge in Perth.

Commissioner Kevin Sleight repealed a 2011 decision imposing a lifetime imprisonment to "TJD." He said that "TJD" could be safely released provided that he will submit himself to a 10-year supervision order.

"TJD" shall wear a GPS tracking device, abide to a night-time curfew and is banned from approaching children unsupervised.

"Although Mr TJD is a serious sex offender, the level of supervision, monitoring and treatment is such that the risk factors identified earlier ... are substantially controlled and minimised," Mr Sleight ruled.

In his decision to release "TJD," Mr Sleight said that great care should be observed to ensure that women shall not fall victim to sexual assaults.

"Great care needs to be taken to ensure that another woman is not the subject of such an attack, which is likely to have long-term and severe psychological consequences," Mr Sleight said.

"TJD" was found to have attacked three women in a span of two days, including raping a 17-year-old girl he threatened at gunpoint in a toilet block. He was then sentenced to a three-year detention by Perth Children's Court.

After being released, he continued with his sexual assaults - raping a teenager at knifepoint in 2000, assaulting an 18-year-old woman in a Perth cemetery while visiting her grandmother's grave in 2003.

He was also released in prison in 2011 under a supervision order that he was always able to break.

Breaching his supervision order, "TJD" failed to take anti-libidinal medication, failed to complete his psychological counselling and used cannabis, and was again jailed.