'A risk': Australia's youngest murderer to be set free

Australia's youngest convicted murderer is about to walk from prison despite a court accepting he poses a risk.

The child killer has spent almost two-thirds of his life behind bars after abducting and fatally stabbing his three-year-old neighbour Courtney Morley-Clarke when he was 13.

His 20-year sentence expired in 2021 but concerns over his stunted maturity, institutionalisation and repeated desire to take violent revenge have led to rare post-sentence detention orders.

He only recently offered a motive for killing Courtney: to exact revenge for purported bullying by her brother.

A brief foray in the community in 2023 on court-ordered close supervision resulted in him approaching about 200 women across 95 days, including several mothers with young children.

He also approached a 15-year-old supermarket worker, blaming a tattoo for his confusion about her age.

One unlawful interaction resulted in an 18-month jail term.

A NSW Supreme Court application to detain him for a further year argued he was "very institutionalised", had suffered a "deep freeze maturation process" and kept ruminating about taking revenge on a community corrections officer who reported his potential breaches.

Psychiatrists have diagnosed the 38-year-old with a severe personality disorder combined with specific social, communication and emotional deficits.

"Given his history of violent behaviour which has involved the use of weapons and planning, he is at risk of engaging in violence of high lethality which could be considered a serious violence offence," a psychiatrist noted in a recent report.

The man's "troubling" sexual focus on young women - "so young that he is able to mistake their age as being 18 or over, when they are not" - was also highlighted in Friday's NSW Supreme Court judgment.

While it was not unlawful to approach an 18-year-old and ask for their phone number to set up a date, it was a matter of concern in the context of the man's risk of sexual offending and capacity to become obsessed about hurting people who "wronged him", Justice Mark Ierace said.

The judge accepted the child killer's prior offending and history of concerning behaviour meant he posed a risk of committing another serious offence.

But he was not satisfied the very high threshold to keep the 38-year-old detained was met, dismissing the NSW government's detention application.

Justice Ierace sided with four forensic experts - two of whom have examined the killer since 2020.

All believe any emerging threat posed by the man to an individual would be detected under the strict supervision regime ordered by a court in 2023.

That regime is due to restart on Saturday when the child killer is released from custody.

The offender is required to stick to a pre-determined schedule of movements, stay off encrypted apps and obey other conditions.

Apart from the brief stint in 2023, he has been in custody since the day he murdered Courtney.

In the middle of a hot summer night, he left his adoptive parents' home on the Central Coast and pulled the girl from her bedroom.

He later told police how he took the youngster to a nearby field.

"I stabbed her in the heart," the then-teenager said, before directing them to a pool of blood on a concrete driveway.

The girl's naked and lifeless body was found in tall grass soon after.

The sentencing judge described the "exceedingly disturbing killing of a very young child" as utterly inexplicable and cruel.

"Somewhat disturbingly he gave one answer (in his police interview) which suggested that, once he had killed one person, he expected that it would become easier killing the next one and the one after that," the judge said.