A young Sydney man who supplied the gun used in the terror killing of police accountant Curtis Cheng will remain behind bars until at least 2029.
Talal Alameddine provided Raban Alou with a pistol that was then given to 15-year-old Farhad Jabar, who shot Mr Cheng as he left work at Parramatta Police Headquarters in 2015.
The 25-year-old refused to stand for Justice Peter Johnson on Friday when he was handed a maximum sentence of 17 years in jail with a non-parole period of 13-and-a-half years.
The NSW Supreme Court judge praised Mr Cheng's widow, Selina, his daughter, Zilvia, and his son, Alpha - who were all present in court - for their "fortitude and dignity".
Alameddine in October 2017 pleaded guilty to recklessly possessing a thing connected with a terrorist act and supplying a pistol. The maximum penalty for both offences is 30 years.
Jabar - also known as Farhad Mohammad - was swiftly killed in an exchange of gunfire with officers after shooting Mr Cheng in the back of the head on the night of October 2.
The court heard officers found a chilling suicide note in the teenager's blood-soaked robes, stating he had "come to put terror in your hearts" by carrying out religious-inspired violence for Islamic State.
"You all are being watched 24/7, while you are asleep, awake, planning," the letter read.
"Your nights will be turned into nightmares, your days into hell ... by the will of Allah."
Alameddine's co-offender Alou was jailed for at least 33 years in March.
Justice Johnson said Jabar and Alou were radicalised extremist supporters of IS while Alameddine had at least some level of sympathy for the "fanatical" organisation.
The judge found the Merrylands man knew the gun was to be used for an immediate terror act but he couldn't determine whether he supplied it for free.
Mr Cheng's widow in March said she was "utterly repulsed" by those who played any role in the murder of her gentle, humble and beloved husband.
"I felt total darkness completely envelope me. I was completely devastated and all sense of security and hope was lost," Selina Cheng told Alameddine's sentence hearing.
Alameddine, who has a criminal history and displayed no remorse, received a 15 per cent sentence discount for his guilty plea, the judge said.
"I am not persuaded the offender has good prospects for rehabilitation," Justice Johnson said.