Police are in the process of charging two men in relation to the murder of veteran police employee Curtis Cheng.
The civilian accountant was shot and killed by radicalised teen Farhad Jabar outside Parramatta police headquarters two weeks ago.
A 22-year-old Merrylands man was arrested on Thursday morning by police attached to the Middle Eastern Organised Crime Squad and investigators from the Joint Counter Terrorism Team in Sydney.
He is expected to face multiple firearms charges and a charge of for hindering police, NSW police commissioner Andrew Scipione said.
An 18-year-old Wentworthville man in custody since October 7 will be charged a commonwealth charge of aid, abet, counsel and procure the commission of a terrorist act.
Both men will face Sydney courts on Friday and are expected to be refused bail.
“Those matters as you would understand are particularly important to the NSW police force having lost one of our own,” Mr Scipione told reporters in Sydney.
“I am angry that we have got a grieving widow and a family who will say goodbye to their husband on Saturday.
“I am encouraged by the fact we have people in custody.”
He said there was much to be done and declined to speculate on whether police were hunting others.
He praised investigative officers for their work.
“This is the sort of tenacity that they bring to this type of crime and it’s a warning to anyone who might choose to get involved with this type of crime,” Mr Scipione said.
“We said it then and we’ll say it now, we will hunt you down.”
Australian Federal Police commissioner Andrew Colvin said police used the full array of laws available to them for the investigation.
The 18-year-old will be charged under section 101 of the crimes act -- a terror related offence which focuses on aiding, abetting, counselling and procurement, Mr Colvin said.
The charge carries a life sentence if proven.
A coroner’s investigation is also underway.
Mr Cheng's funeral is due to be held at Sydney's St Mary's Cathedral on Saturday morning.
On Thursday Prime Minister Malcolm Turnbull opened a counter terror summit in Canberra by urging authorities to experiment to find better ways of combating extremism.