Mr Grant, who is also the Minister for Police, said his heartfelt condolences went out to the family of the police employee killed.

The victim has been named as Curtis Cheng, a 17-year veteran of the NSW Police Force.

Only scant details have emerged about the 15-year-old who shot and killed Mr Cheng as he left work at the State Crime Command on Friday afternoon. Police have refused to confirm his identity until they've completed "all formalities" but he has been named in media reports as Farhad Khalil Mohammad Jabar of Iraqi-Kurdish background and born in Iran.

Commissioner Andrew Scipione says investigators are still a long way from establishing a full picture of the teen but "his actions were politically motivated and therefore linked to terrorism".

At this early stage, Mr Scipione says his investigators have no information to tie the boy to a specific group.

The Commissioner said there was nothing to suggest he was doing anything but acting alone.

The Deputy Premier expressed his sympathy for the family of Mr Cheng and to all officers in the NSW Police Force.

"A member of the NSW police family was killed yesterday afternoon, a scenario that has left me and the entire police community shocked and deeply saddened," Mr Grant said.

"The death of any member of the NSW Police Force is a tragedy but when it is under circumstances such as this, it is even more devastating.

"My heartfelt condolences go out to the family of the police employee killed in Friday's incident.

"This event will have an overwhelming impact on the officers and police employees in the Parramatta area and my condolences go to them as well.

"I am proud of the bravery and swift action the Special Constables demonstrated, risking their own lives in the protection of others.

"This will be a complex investigation and I have every confidence in the professionalism and dedication of the NSW Police Force to investigate this incident.

"This is a horrendous tragedy just days after we paid tribute to the men and women of the NSW Police Force for National Police Remembrance Day.

"Sadly this is a risk the men and women of the NSW Police Force face every day and I extend my deepest sympathy to all officers, sworn and unsworn, across the state."

A police source said there had been increased "chatter" detected in the past week relating to a possible attack on the Parramatta headquarters.

The officer, who works at the State Crime Command headquarters, said every officer had been ordered to wear their guns on them at all times this week, even while at their desks.

An alert was circulated to all police officers on Friday night detailing what had occurred at Parramatta and urging them to remain vigilant, particularly around police stations.