His usual "happy disposition" was replaced with depression and frustration.

That evening, still dressed in his fluoro vest four hours after leaving work on June 19, 2013, he stopped on a street near his parents' Hunters Hill home and followed a young woman.

The 30-year-old Thai woman, who cannot be identified, was listening to music through headphones after finishing a babysitting shift on Sydney's north shore.

Leary, 49, put his arm around her neck, dragged her behind a bus shelter and unleashed a ferocious attack.

Despite her kicking and screaming, he punched her in the face several times and pulled her jeans down with such force that her belt snapped. He used a knife to stab her in the neck before a passer-by called police.

On Tuesday, Judge Helen Syme sentenced Leary in the NSW District Court to a maximum 15 years jail for recklessly causing actual bodily harm with intent to have sexual intercourse – an offence with a maximum penalty of 20 years.

She gave him another chance to apply for parole in 2024, after serving 11 years and three months of the term.

Leary was already on parole after serving 22 years for killing teenager Vanessa Hoson in 1990. He broke into her family's Kenthurst house and bashed her to death with a hammer after she refused to have sex with him.

Ms Hoson's family campaigned against his release in 2012, fearing he would attack again.

On Tuesday, Ms Hoson's brother-in-law, Chris, shouted at Leary as he was taken from the dock, "Hang yourself Leary, hang yourself you coward".

Leary, a short man with receding grey hair and glasses, showed no emotion and didn't look away from the judge as she handed down her sentence.

Judge Syme said there were disturbing similarities between the two crimes. Both were spontaneous outbursts, motivated by sexual desire and a loss of control when sex was not offered. Both involved "extreme and explosive violence".

She took into account his guilty plea and the fact he had completed several rehabilitation programs in prison and obtained a bachelor of arts by studying sociology and anthropology.

However, she said Leary was still a danger to the community because no one could be sure he wouldn't suffer another outburst. She said his eventual parole will require a "significant alteration" of the supervision regime.

"His unpredictability makes his management in the community a challenge," she said. "Not all forms of antisocial behaviour can be treated through therapy."

On the day his workmates noticed a sudden change, Leary was suffering from several forms of "acute stress".

His parole officer had visited him two weeks before the attack and found him to be stable and enjoying his job.

However, he was feeling a growing dissatisfaction, believing the work was beneath his intellect and his bachelor degree.

A Thai woman who he had married while in prison, in an unsuccessful attempt to get her permanent residency, had moved back to Thailand and tried to distance herself from him, despite him still sending her money.

"Her response left him feeling inadequate, angry and frustrated," Judge Syme said.

He was coming to terms with being deprived of his "strong desire to have a family", compounded by his impotence and long-held relationship issues stemming from a serious sexual abuse by a Catholic brother when he was 10 years old.

Judge Syme said it was probably not a coincidence that he chose to attack a Thai woman that night.

The woman tried at first to offer Leary her phone and bag. When she realised he was attempting to rape her, she pretended to submit, saying, "It's OK, I know what you want, I will help you" and touching his face, however, Leary bit on her finger.

He punched police officers when they arrived, even after they deployed capsicum spray and a Taser.

His victim spent a week in hospital and has ongoing psychological issues, the court heard.

Outside court, Ms Hoson's sister, Fiona, said they were incredulous that Judge Syme gave Leary another chance at parole.