Authorities believe 15-year-old shooter Farhad Jabar was recruited by western Sydney extremists 'in the same way a pedophile would groom a victim' to carry out a terrorist attack on Parramatta police headquarters.
Fairfax reports new CCTV being investigated by police shows a number of men meeting the young boy in the hours before the deadly attack on Curtis Cheng, the 58-year-old police accountant killed by a single gunshot to the back of the head.
Police believe Jabar was recruited by other figures because they were under too much surveillance to do it themselves.
"What we're finding is that they're targeting younger and younger people, so that remain a great concern to Australian authorities," he said.
"We already know what while ISIL exists in the middle east they will continue to export terror into Australia," Federal Justice Minister Michael Keenan told Sunrise.
Extremists use a very sophisticated social media campaign that sends out over 100,000 messages a day, Minister Keenan said.
"They seek to identify vulnerable people and they groom them - in the same way a pedophile would groom a victim - to carry out a terror attack in here in Australia."
Police are investigating whether a Middle Eastern crime gang is behind Jabar being given the older-style handgun used in last Friday's tragedy.
A known crime figure is believed to have been responsible for the .38 Smith and Wesson ending up in the hands of Jabar.
The 15-year-old boy was carrying the gun along with a letter in his Nike backpack warning of the terror attack.
The letter was discovered in the bag outside the school on Friday containing the words "let the blood flow on the street" with other 'extremist' language but it did not contain any details about specific targets, the Daily Telegraph reports.
Police confirmed the supply of a firearm to the teenage terrorist is central to the investigation of Mr Cheng's murder.
Deputy NSW Police Commissioner Catherine Burn confirmed five arrests were made in raids across homes in Sydney's west from 6am this morning in relation to the fatal shooting of Curtis Cheng, with four people currently in custody.
The fifth man, a 24-year-old man from Merrylands, was not detained as part of the operation but was arrested as a result of an outstanding warrant for identity fraud.
Three of the four people arrested in pre-dawn raids in Sydney's west have been released from custody as investigations into the killing of NSW police employee Curtis Cheng continue.
An 18-year-old man who was arrested at a home in Wentworthville remains in custody.
More than 200 heavily armed officers from the NSW counterterrorism squad, homicide squad and AFP raided houses in Guildford, Wentworthville, Merrylands and Marsfield.
One of the homes raided was the same house where Omarjan Azari was arrested in Guildford in September last year over an alleged plot to behead a random member of the public.
Azari is charged with conspiring to commit acts in preparation of a terrorist attack.
Two other homes targeted in Wednesday morning's raids in Marsfield and Wentworthville were also raided in September last year, with some of the same men taken back into custody.
Investigators have closely examined security footage from a 15-year-old's attack on a Parramatta police station.
Their investigation shows Farhad Jabar was at first following a female detective out of the building.
He is seen to walk closely behind her but it appears she was too quick for him as she was power walking.
Moments later he picked Curtis Cheng as his target – a life and death decision.
Exclusive footage obtained by 7 News shows 15-year-old Farhad Jabar walking along Church Street, dressed in a black robe he changed into after praying at the mosque.
The video shows the radicalised teenager waving a gun and shouting at police, while young children played at the Good Start daycare centre just metres away.