Curtis Cheng (pictured) was shot dead at the front of NSW Police HQ in 2015

A radicalised Muslim who supplied the firearm used to kill police accountant Curtis Cheng in a terror attack has been sentenced to 44 years in jail, but not before giving the judge a middle finger salute.

Raban Alou pleaded guilty to aiding, abetting, counselling or procuring the terrorist act by Farhad Jabar, who fatally shot Mr Cheng outside NSW Police Headquarters in Parramatta in 2015.

The 20-year-old gave a one-finger salute to the court and yelled: 'I'm going to paradise, you're going to hell... this is just the beginning for enemies of Islam'.

Alou was sentenced to a non-parole period of 33 years on Thursday.

His sentencing comes little more than a month after Alou refused to stand for a NSW Supreme Court justice, despite being told there could be repercussions for not doing so.

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Raban Alou (pictured), who supplied the firearm used to kill police accountant Curtis Cheng in an act of terrorism in 2015, has been sentenced to 44 years jail

Curtis Cheng's son Alpha Cheng (right), and widow Selina Cheng are seen leaving court on Thursday

Redacted crown documents previously alleged Alou supplied and loaded the gun for 15-year-old Jabar at a nearby mosque before the killing on October 2.

Jabar was shot dead in a hail of gunfire minutes after the shooting of Mr Cheng.

Justice Peter Johnson said that Alou's outburst in court on Thursday proved that the chances of him being rehabilitated from his radicalisation were 'almost hopeless'.

Crown prosecutor Paul McGuire SC earlier this year told the NSW Supreme Court of Alou's lack of remorse, his extremist views and poor prospects of rehabilitation.

He will not be eligible for parole until 2048.

Alou (pictured during his arrest) was unmoved in court in Januray when told by Justice Peter Johnson there could be repercussions for refusing to stand during his indictment for religious reasons

The 20-year-old threatened corrective services officers and firefighters when there was a blaze at the prison, and made a hand gesture associated with Islamic State.

Alou gave the gun to Jabar at Parramatta Mosque and from there he walked to Police Headquarters and shot Mr Cheng dead as he left work.

Three other males have been charged in relation to the killing of Mr Cheng, who died instantly after being shot in the back of the head as he left work.

The Crown previously alleged that Jabar walked back and forth while yelling 'Allahu Akhbar' in the moments before he was shot dead by detectives.