NSW Police sources have confirmed that a 15-year-old boy was the lone gunman who shot dead a police employee outside the state's headquarters in Sydney's west.
The teenager shouted religious slogans before firing one shot in the back of the head of a police IT worker as the employee was heading home on Friday afternoon.
The shooting took place outside the State Crime Command in Parramatta, home to the state's homicide, drug, Middle Eastern organised crime and gangs squad, located near a primary and high school.
It is understood some members of the gunman's family had just returned to the Middle East.
NSW Police Commissioner Andrew Scipione said the gunman then remained on the street and was acting "aggressively" before he was shot and killed in a shoot-out with special constables responding to the initial shooting.
Footage of the incident was captured on security cameras.
"An employee of the NSW Police Force has been callously murdered here today," Mr Scipione said on Friday night.
"This is a very sobering time for us ... I can tell you that this was a brutal crime. It was a terrible crime."
Mr Scipione would not rule out any links to terrorist related activities on Friday.
He said he had viewed footage of the shootings and said there was nothing to link this event to "any terrorist-related activity but we could not say that that wasn't the case".
"The footage that I've viewed shows that this particular man was certainly targeted," he said. "Certainly [the gunshot] was very close range."
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 that 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.
With Ava Benny Morrison and Rachel Olding