Milad Atai was sentenced on Friday for assisting and encouraging 15-year-old Farhad Jabar to shoot Mr Cheng at the state police headquarters at Parramatta in 2015 and helping the boy's sister reach Islamic State in Syria.

In jailing the 22-year-old for a total of 38 years, NSW Supreme Court Justice Peter Johnson said Atai was a supporter of extreme jihad for many months before the terrorist attack and appeared to still hold radical views.

As he was led away from court, Atai raised his index finger in the direction of the judge and shouted in a foreign language.

His barrister earlier told the court the former plumber would not stand when he was sentenced, as is customary.

"That itself is an indication of his current thinking, which is regrettable," Justice Johnson said.

Justice Johnson said while Atai did not play the critical role of passing to Jabar the gun used to kill Mr Cheng, he was well aware of the plans and made no attempts to dissuade the boy.

Further, as the self-described best friend of the attack's key plotter Raban Alou, Atai attended several meetings across Sydney's west and offered use of his own phone as Alou tried to get Jabar a gun.

Justice Johnson said he didn't accept Atai's claim that he thought the attack had been called off.

By his own evidence, Atai said had he known the attack was going ahead on October 2, he would have made sure he'd have attended to help Alou, the judge said.

Atai also played a significant organisational role in helping to get Jabar's sister to Syria, including giving her $1000 for flights and advice on the route and clothing to take to avoid detection.

Australian Associated Press