Australia’s youngest-ever convicted murderer will walk from prison following a court’s refusal to keep him locked up four years after his sentence ended.

His 20-year sentence expired in 2021 but concerns over his stunted maturity, institutionalisation and threats of inflicting violence against others have led to rare post-sentence detention orders.

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.

One unlawful interaction – talking to a mother dressing her young child at a beach – forced his return to jail.

An application to detain him for a further year was heard in the NSW Supreme Court as the state argued he posed too great a risk to the community.

Concerns were aired the man was “very institutionalised”, had suffered a “deep freeze maturation process” and kept ruminating about taking revenge on a community corrections officer.

Psychiatrists previously diagnosed the 38-year-old with a severe personality disorder that made him self-centred and unempathetic.

But Justice Mark Ierace on Friday dismissed the state’s application to detain the killer further.

His written reasons are expected to be published later in the day.

It likely means Courtney’s killer falls back onto his prior extended supervision order, requiring him to stick to a pre-determined schedule of movements, stay off encrypted apps and other conditions.

The order runs the maximum five years.

He entered custody the day he murdered Courtney, having left his adoptive parents’ home on the Central Coast in the middle of a hot summer night before pulling 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.

The boy then directed police to a pool of blood on a concrete driveway and a steak knife lying nearby.

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.