Court documents have revealed the full details of the April 2017 rampage of the teenager and his accomplice, who cannot be named for legal reasons, which included the murder of Zeeshan Akbar.

The pair were 15 and 16 at the time when they stabbed the 29-year-old three times and left him to die in a pool of blood inside a Queanbeyan Caltex.

They will be sentenced in April after last year pleading guilty to murder as well as a string of other charges related to their slew of crimes on the evening of April 6 and morning of April 7.

After the Pakistani student let the pair inside the Bungendore Road service station about 11.46pm, the offender, who can only be identified as DM and was 16 at the time, stabbed him in the back.

The other teen, known as DS, jumped the counter and attempted to remove a cash register while DM continued to stab Mr Akbar at the rear of the store.

"(DM) approached Akbar who was lying on the floor, (DM) dipped his finger in Akbar's blood, walked to the glass window, and wrote the letter 'I' on it," the statement of agreed facts said.

"He then returned to Akbar, once again dipped his finger in his blood, walked to the glass window, and wrote the letter 'S'."

The pair made off with a cash register and cigarettes.

Crown prosecutor Mark Hobart SC told a NSW Supreme Court sentence hearing on Friday the crime was chilling and "one of the worst I've ever seen".

The murder was captured on CCTV and Justice Geoffrey Bellew refused to release the footage to the media because it was so disturbing.

Justice Bellew described Mr Akbar as someone who came to Australia and "made every post a winner".

Earlier in the night, DM told friends he had "joined ISIS" and showed them a picture on his phone of a man standing beside a severed human head.

When he was arrested, he yelled out: "Allah Akbar, Allah Akbar, I'm going to cut your heads off".

In his cell at Queanbeyan Police Station he scrawled "IS" on the wall in tomato sauce.

However, the court heard DM, who was diagnosed with schizophrenia and was suffering auditory hallucinations, no longer adhered to the views of the extremist Islamic group.

"He seems to have been de-radicalised as quickly as he became radicalised," DM's barrister Thomas Jones told the court.

"I don't know what to make it."

After smoking cannabis earlier in the night, DM and DS went on a crime spree around Queanbeyan which began with attempting to rob a liquor store attendant and glassing a man they met sitting on a park bench.

After stealing the man's longneck beer bottle, DM smashed it on the side of his head.

They also attempted to rob a 41-year-old man when they went to his house and, after being invited in, they threatened him with a knife.

The morning after killing Mr Akbar, the pair hailed a passing motorist who DM stabbed in the chest before stealing his car.

The man suffered a collapsed lung and DM has pleaded guilty to intent to cause grievous bodily harm.

Their crime spree ended after a police pursuit when they were caught on the Monaro Highway in the ACT.

Australian Associated Press