A teenager remains in custody tonight after four people were arrested in Sydney’s west, over the murder of a police accountant.

Detectives are investigating whether more students are known supporters of Islamic State.

Bianca Banchetti reports.

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Police have reviewed security video from Parramatta Mosque.

The footage shows 15-year-old Farhad Jabar with several men just hours before carrying out the shooting at Police Headquarters last Friday.

Detectives believe Jabar was given the handgun at the mosque before the attack.

A Middle Eastern crime gang is being investigated over possible links to the weapon.

Four men were detained in a series of dawn raids, Wednesday morning.

Three of them, including 16-year old classmate of the teenage shooter, were released from custody late yesterday, without charge.

An 18 year old remains in police custody, as investigations continue.

In the wake of Curtis Cheng’s murder there’s renewed concern about what is happening to young minds in schools.

New South Wales Premier, Mike Baird has ordered work on counter radicalisation to be fast tracked.

Bianca Banchetti, QUT News.