A 16-year-old boy brutally stabbed a petrol station attendant to death before writing the initials "IS" in blood on the store window.

Key points: Zeeshan Akbar was stabbed multiple times at the Queanbeyan petrol station where he worked in 2017

Zeeshan Akbar was stabbed multiple times at the Queanbeyan petrol station where he worked in 2017 The two youths, then aged 15 and 16, who murdered him pleaded guilty and will be sentenced in April

The two youths, then aged 15 and 16, who murdered him pleaded guilty and will be sentenced in April A judge has decided not to release CCTV footage of the attack as it is too graphic

Details of the slaying emerged in court documents lodged today in the New South Wales Supreme Court during sentencing for the teenager and his younger co-accused.

The pair pleaded guilty to murdering Pakistani national Zeeshan Akbar at a petrol station in Queanbeyan, just outside Canberra in April 2017.

The youths, who were 15 and 16 at the time of the crime, sat separated by two corrections officers in the Sydney court.

Prosecutors called for a strong sentence to reflect the "savagery" of the killing.

The court heard Mr Akbar had fought for his life as the older boy stabbed him repeatedly, while the other teen stole cigarettes and the till.

Prosecutors said the intention to kill had been formed at some point, with Justice Geoffrey Bellew noting a comment the older boy had made earlier in the day when he armed himself with a knife.

"If anyone gets in my way, I'll stab them," he had said.

Prosecutors said he continued to be a danger to the community.

The older boy's barrister, Tom Jones, said his client had been in a psychotic state but that had eased with medication in custody.

"He feels a lot more stable. He feels a lot better," Mr Jones said.

But he acknowledged his client, who had been diagnosed with schizophrenia when he was 15, remained a work in progress.

The CCTV footage from Caltex service station in Queanbeyan is so graphic the court will not release it. ( ABC News: Jake Evans )

Mr Jones also asked the court to consider the teen's upbringing, which he said was marred by alcohol abuse, drugs and a seriously violent father.

Barrister Scott Corish, who represented the younger offender, said his client knew he would be in jail for a long time.

But he asked the court to take into account the fact that the boy had played a secondary role, though he said he was not trying to minimise the involvement.

Mr Corish also requested that the court consider a special provisional sentence, which can be imposed on serious offenders who are under 18, saying he met the criteria.

"He does have and did have a cognitive impairment," the barrister said.

"His lower level of intelligence is a matter of cognitive impairment."

Justice Bellew rejected that idea but the court may still consider an alternative — keeping the youth in detention until he is 21, delaying his time in an adult jail.

Zeeshan Akbar (in the blue shirt at the rear) and his social cricket team in Canberra. Mr Akbar was fatally stabbed while he worked at a Queanbeyan service station in the early hours of Friday April 7, 2017. ( Supplied )

Murderer's link to terrorism 'momentary': defence

One of the curious issues in the case was the suggestion the older offender was linked with terrorism. He had scrawled IS — a commonly used shorthand for Islamic State — on the service station window.

When he was arrested, he shouted, "Allah akbar, Allah akbar … I am going to cut your heads off … There is only one god."

Before the killing, the then 16-year-old showed other people messages between himself and what one of his companions described as "an Arab dude".

He later scrawled IS in tomato sauce on his prison cell wall.

But his lawyer played down the link, saying it appeared to be momentary.

"He seems to have become deradicalised as quickly as he was radicalised," Mr Jones said.

CCTV footage too graphic to be released

Both teenagers have pleaded guilty to the 2017 murder at the Queanbeyan service station. ( ABC News: Elise Scott )

The court documents released today revealed Mr Akbar was killed after a string of other crimes during a rampage through Queanbeyan in southern NSW and across the border in Canberra.

The court heard the pair had been with a larger group earlier in the evening at the home of the older boy, and down near the Queanbeyan River later.

The larger group was involved in an attempted robbery of a liquor store and an assault on another man.

The two accused were also involved in an assault and an attempted robbery at a home.

By the time they went to the petrol station, there were only two of them.

Justice Bellew said the CCTV footage of the attack was so graphic it would not be released.

Hours after the murder of Mr Akbar, the two teenagers waved down a car, stabbed the driver and stole his vehicle after telling him they had killed someone.

The pair were finally caught after a police chase through Canberra.

Mr Akbar's family were not in court today though they attended earlier hearings, travelling from Pakistan.

The two youths are due to be sentenced in April.