Berwyn Rees pleaded guilty to the murder of Sergeant Keith Haydon as well as those of Raymond James and Christopher Greenfield.

During a 1977 Bondi gun robbery, he murdered Mr James and Mr Greenfield by shooting them at close range. Later, it was target practice in Hunter bushland with guns taken in that hold-up that ultimately drew Sergeant Haydon to investigate reports of shots fired in November 1980.

Rees, who was on the run, shot and killed Sergeant Haydon before subsequently firing on another officer, Constable Alex Pietruszka. Constable Pietruszka survived his injuries.

The decision to let Rees walk free after decades behind bars has been blasted by the Police Association of NSW, who described his offences as "brutally ruthless".

"Allowing him to walk free when it was originally judged that his sentences should be served for the balance of his natural life, is a gross injustice to the victims and their families," association president Tony King said.

"What does this say about the loss of life of the two men Rees killed in an armed robbery in 1977, and the murder of Sergeant Keith Hayden and serious wounding of Constable Alexander Pietruszka he went on to commit in 1980?

"No one who shot and killed a serving police officer should ever have the benefit of rejoining society and walking freely around the streets.

"This disgraceful parole decision is an insult to the memory of the victims and shows no regard for the importance of their lives."

NSW Corrections Minister Anthony Roberts said he was "extremely disappointed" with the decision.

"The NSW government and Commissioner of Corrective Services NSW have both opposed his release to parole," he said. "I am seeking legal advice to determine the State's ability to appeal this decision. As a consequence, at this time it would be inappropriate for me to comment further."

It is not the first time Rees has approached freedom. In February this year, a decision to give Rees parole went to the state's highest court amid condemnation from the police union and then NSW Corrections Minister David Elliott, who sought legal advice to appeal.

NSW Supreme Court Justice Richard Button in May quashed that parole approval for the then 69-year-old. Justice Button said the parole authority had considered the physical threat to the victims' families but its decision should "also encompass the psychological or emotional effects".

Rees was initially sentenced to three life sentences, which in 1993 were redetermined. For the Sydney murders he was set a minimum term of 18 years and for Sergeant Haydon's murder he was sentenced to a minimum of 27 years.

That longer sentence ended in 2007, when he became eligible for parole, but the additional term on each of the three sentences was life.

Tracy James, who was two when Rees shot her father, told a Sydney radio station that the decision to again offer parole left her "completely speechless".

"To let out a triple murderer by saying he's been so good in jail ... it's wrong," she told 2GB.

A summary of Rees' application for parole earlier this month notes that the authority cannot grant parole "unless it is satisfied that it [is] in the interests of the safety of the community to do so".

It notes that Rees became eligible for parole in 2007 and that expert reports contended that his risk of recidivism was lower than ever partly due to "the deteriorating state of health of the offender, then 69 years of age; to his gout, vision problems, obesity, kidney problems and rheumatism of knees and hips".

The summary notes Rees lived a "purposeless and frustrating life" before committing his crimes. "During his early years in custody, he realised that he needed to change and engage in worthwhile activities but it took him until about 1985 to will himself to do so," it states.

The decision on Rees comes a year after Sergeant Haydon was posthumously recognised for distinguished service. His son, Peter, described hearing of his father's death as a 14-year-old. "I thought it's not dad, because he's got the day off. As I found out later, he had swapped his days of work with the other policeman there at the station," Mr Haydon said in 2018.

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