A South Australian judge has found it is "significantly likely" that a serial rapist who preyed on women in the 1990s could attack again if released from prison — but will not lock him up indefinitely.

Key points: Joseph Maxwell Duroux is currently serving a 28-year jail sentence

Joseph Maxwell Duroux is currently serving a 28-year jail sentence He was convicted of rape and attempted rape during the 1990s

He was convicted of rape and attempted rape during the 1990s But an SA judge says the risk if he is released is "not immediate"

Justice Martin Hinton said Joseph Maxwell Duroux still had time to "address his criminogenic factors and begin the deinstitutionalising process".

"The prospects may not be great, but the stakes for Mr Duroux are high," he said.

Duroux is now institutionalised, having been jailed for all but two-and-a-half years since 1988.

The 54-year-old is currently serving a 28-year jail sentence for seven counts of rape against three women in 1991 and one attempted rape in 1995 that occurred during break-ins across Adelaide.

He has been eligible for parole since April 2015 and is due for release in June 2025.

Judge says risk if released is 'not immediate'

South Australian Attorney-General Vickie Chapman applied to the Supreme Court for Duroux to be indefinitely detained because he could not control his sexual instincts and posed a risk to the community.

The application was made to pre-empt a bid for parole.

Ms Chapman applied to the Supreme Court for Deroux to be indefinitely detained. ( ABC News: Nick Harmsen )

But Justice Hinton rejected the application, finding there was still time for the prisoner to work with psychologists to gain victim empathy and to better understand the consequences of his actions.

"Further, psychologists could undertake cognitive behavioural work with him to equip Mr Duroux with better ways of coping with life and with his emotions," he said.

Justice Hinton found that Duroux — who suffers from schizophrenia — was unable to control his sexual instincts but said his risk, if released, was "not immediate".

"The evidence does not support a conclusion that he is likely to immediately set about planning to rape vulnerable women," he said.

But he said if he was to develop "maladaptive behaviours as a means of coping with life stresses" — as he had in the past — his risk to the community increased.

"It is the likelihood of his developing those maladaptive behaviours that renders it significantly likely that he will sexually offend in the future," he said.

Sometimes the risk is 'too great'

He said if he was "wrong" in that assessment and Duroux's sexual offending was "premediated" and committed after ensuring victims would be alone and vulnerable, then his risk — "likely borne of deviant sexual fantasies" — was only greater.

"There is an unfortunate paradox here … our system of criminal justice and punishment is intended, in the vast majority of cases, to ultimately result in reclaiming the offender," he said.

"Here, the 2001 sentencing judge set a non-parole period in expectation that, in Mr Duroux's case, that would occur.

"And yet the sentence has resulted in Mr Duroux's institutionalisation, which in no small part contributes to the position [in which] he now finds himself."

He said the Department of Corrections recognised this and through many programs, attempted to help prisoners to re-socialise and reintegrate back into the community.

"However, sometimes the risk posed by an offender is too great. Such cases are rare and exceptional," he said.

"Is this one? Or, perhaps, can it be said today that it is one?"

Justice Hinton quoted the late Sir Leon Radzinowicz, QC — the founding director of the Institute of Criminology at Cambridge University and a prominent academic — in his decision.

Sir Leon stated: "Unless indeterminate sentences are awarded with great care, there is a grave risk that this measure, designed to ensure the better protect of society, may become an instrument of social aggression and weaken the basic principle of individual liberty".

Following the findings, Attorney-General Vickie Chapman said in a statement she was "considering the judgement".