A Sydney man who appeared to be hours away from being released from custody has been charged with helping teenager Farhad Jabar murder NSW police accountant Curtis Cheng.
The 18-year-old now faces a Commonwealth terrorism offence, which carries a maximum term of life imprisonment.
His 16-year-old brother was in Year 10 at Arthur Phillip High School with 15-year-old Jabar.
The Wentworthville man had been on remand since counter-terrorism raids in Sydney's west last week following the terror shooting outside police headquarters in Parramatta on October 2.
The Australian Federal Police successfully applied to keep him in custody for 100 hours and were granted another 68 hours to interview him on Monday.
Police had until Thursday afternoon to charge or release him.
A second man, 22, was also charged with supplying the gun that Jabar used to kill Mr Cheng, breaching a firearms prohibition order and hindering police.
He was one of the four males detained in the raids last Wednesday, but was released before being arrested again on Thursday morning in Merrylands.
NSW Police Commissioner Andrew Scipione described the breakthrough as a "significant development".
"Today is the culmination of hundreds of hours of work by our officers ... but there is much work still to be done," he said.
Mr Scipione said it will be a "lengthy investigation".
"I am encouraged we have people in custody but my thoughts continually go out to Curtis's wife," he said.
He said he would not speculate on whether the man was working for a terrorist organisation.
The 22-year-old will face Parramatta Local Court on Friday and the 18-year-old is due at Central Local Court.
Mr Cheng's funeral is due to be held at Sydney's St Mary's Cathedral on Saturday morning.
