An audit of prayer groups in New South Wales' public schools has now been completed and its results are being considered by the State Government, amid concerns of extremist Islamic preaching.

Premier Mike Baird announced the audit in July after it was reported that a student at Epping Boys High in Sydney may have preached extremist interpretations of Islam during lunchtime prayer sessions.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 8 minutes 59 seconds 8 m More terror arrests and police asked how a teen killer slipped their net ( Sean Rubinsztein-Dunlop and Dylan Welch )

A spokeswoman for the NSW Education Minister said the audit looked at all public schools including Arthur Phillip High - the school attended by teenage gunman Farhad Jabar who carried out Friday's fatal attack on the police headquarters at Parramatta.

Yesterday, four males were arrested in raids across western Sydney during investigations into the fatal shooting of police accountant Curtis Cheng.

Two of the males arrested, along with a teenager charged with threatening police on Tuesday, and 15-year-old Jabar were all current or former students of Arthur Phillip High school.

Yesterday, the Premier said radicalisation among students was not a widespread problem, but he had asked the Education Department to accelerate the work it was doing to combat it.

Federal Justice Minister Michael Keenan today told Channel Nine that the Government was taking the issue seriously.

"We're working with NSW education authorities to make sure that teachers actually have the ability to identify if somebody under their charge is going through a process of radicalisation," he said.

A student on his way to Arthur Phillip High School was arrested on Tuesday after allegedly threatening police. ( ABC News: David Spicer )

A Western Sydney community development worker told 702 ABC Sydney that the issue of youth radicalisation had sat under the radar for more than a decade as young people became more isolated.

Sarkis Achmar said while young people have always sought a sense of belonging, extremist groups are capitalising on those typical teenage sentiments because traditional community and religious ties are on the wane.

"There's a void in their life. You can fill it with activities, you can fill it with courses, you can fill it with sports," he said.

"But when they're lying down in bed at night there's still that emptiness that's going on and when somebody encapsulates that sense of 'you belong with us, we've got your back, whatever you need, let's hang out, let's have a laugh,' they get drawn to that because they're not getting it anywhere else."

Justice Minister urges public patience

Mr Keenan also urged the public to allow police the space and time they need to investigate the killing of Mr Cheng.

Three of four males arrested on Wednesday morning over last week's terrorist attack were targeted in Australia's biggest counter-terrorism raids a year ago.

Police said the 15-year-old gunman Farhad Jabar was politically motivated and had links to terrorism. ( Instagram )

Only one arrested yesterday is still in custody being questioned. The three others arrested were released without charge.

Mr Keenan has denied that authorities dropped the ball.

"People need to know that the police are pursuing their lines of inquiry and they will do so diligently and methodically and they are very good at what they do," he said.

"The most important thing is that anyone involved in this horrendous murder is held to account for their crime.

"The police are going through that process and obviously they'll be able to update the Australian people once that's concluded and they will hold people to account."

Supply of gun probed by police

More than 200 police officers were involved in the counter-terrorism raids across western Sydney yesterday morning in which the four males aged between 16 and 22 were arrested.

More than 200 police officers were involved in raids across western Sydney yesterday. ( Supplied: NSW Police )

Police said yesterday, the four males were being investigated over links to the Parramatta police headquarters attack.

Officers said the 15-year-old gunman did not act alone and are investigating where the gun came from and whether one of those arrested supplied it to Jabar.

During the raids, police returned to the Guildford home of Omarjan Azari, who is in jail on a charge of conspiracy to murder after being arrested in last year's raids.

The 2014 raids were sparked by a phone call to Azari in which Australia's most senior Islamic State lieutenant, Mohammad Ali Baryalei, allegedly directed him to kill a random member of the public.

Floral tributes are laid at Parramatta Police headquarters following the death of Curtis Cheng. ( ABC News: Mohamed Taha )

Members of the group who were raided in 2014 and Baryalei, who has since been killed in Syria, were known to congregate at the Parramatta mosque where Jabar spent several hours before he carried out last Friday's attack.

The 15-year-old was shot and killed by police at the scene of the shooting.

In a statement, the family of Mr Cheng expressed their gratitude for the "overwhelming sympathy and support" from the public, the Government and Mr Cheng's police force colleagues.

"The family says it appreciates the respect shown to it by media organisations and asks for that privacy to continue," the statement, issued by NSW Police, said.

The statement said Mr Cheng's family were finalising arrangements for his funeral.