A group of extremists may have recruited teenager Farhad Jabar to carry out the Parramatta shooting because they were under too much surveillance to do it themselves.

Police have seen CCTV footage from a Parramatta mosque, showing Jabar talking to several men hours before he shot dead accountant Curtis Cheng, 58, Fairfax Media reported on Thursday.

“Some of them might have been wanting to do an attack but were concerned. They’ve managed to radicalise a poor vulnerable person to do it instead,” a police source told Fairfax Media.

“It’s almost like they’ve groomed him like paedophiles to do something for them.”

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Authorities reportedly believed Jabar was supplied with a handgun at the mosque that afternoon, which he concealed in his backpack.

A Middle Eastern crime gang was reportedly being investigated by police for supplying the weapon.

Minister for Immigration and Border Protection Peter Dutton told 2GB on Thursday his department were investigating those who may have helped the teen shooter.

On Wednesday morning, more than 200 police raided homes across Sydney’s west in relation to the execution on Friday.

Four of the five men arrested have been released by police without charge.

During the raids Talal Alameddine, who had previously been on firearms charges, was detained at a home but police don’t believe he sourced the gun, reports said.

Others arrested included, a man from north-west Sydney and two brothers, aged 16 and 18, from Wentworthville.

The man from the north-west and the Wentworthville brothers had previously been targeted in Operation Appleby anti-terror raids in September 2014.

Omarjan Azari, 23, and Islamic State recruiter Mohammed Ali Baryalei were at the centre of the Appelby raids for discussing an alleged plot to behead a random person in Sydney.

The men targeted in Operation Appleby gathered at Parramatta Mosque regularly. Two of Mr Azari’s brothers were targeted, but not arrested, in the raids on Wednesday.

The men been under heavy surveillance since the 2014 raids, reportedly forcing them to look for alternative ways to carry out an attack, Fairfax Media reported.