The chairman of Parramatta Mosque, Neil El-Kadomi, delivered this blunt message to hundreds of his faithful on Friday, one week after their fellow worshipper, 15-year-old Farahd Jabar, shot dead a police employee.

Mr Kadomi told those gathered for Friday prayers that Australia had given them endless opportunity and freedom, which many of their brothers and sisters overseas could only hope for.

​"My message to those who would consider committing an act of violence is it will not be tolerated," he said.

As Mr Kadomi uttered those words, the older brother of an 18-year-old man who police believe supplied the gun to Jabar, sat motionless on the red-carpet floor.

The 22-year-old Wentworthville man, who cannot be named for legal reasons, was himself the target of the largest counter-terrorism raids in the nation's history last year. On Tuesday he was also arrested before repeatedly taunting the media as he swung his car in and out of his driveway at his family's home on Lane Street, Wentworthville.

He is also the brother of the 16-year-old Arthur Phillip high student who police believe recruited Farahd Jabar into extremist lunchtime prayer groups.

Mr Kadomi issued a stern warning to the 22-year-old's family.

"No one should take their freedom, safety and acceptance for granted," he said

Hundreds nodded in agreement, from brickie to finance worker. They had assembled for the midday prayer of Duhr.

Mr Kadomi spoke of the anguish of the community following Farahd's spiral into extremism that ended with his execution of police accountant Curtis Cheng.

"None of us could ever imagine that such a thing could happen. The whole community grieves over this tragic incident."

"This tragedy has shocked us all and brought to light an issue...that we must act on."

He said he was ashamed that his mosque, where it is believed Jabar obtained his deadly weapon, had been searched by police.

"I'm not hiding anything, see in the mosque, there are no guns," he said.

Mr Kadomi said: "I need a safe street for my wife and children.

"I want to remind us all of the importance of listening to our children so that they do not lose hope and a sense of purpose."

Parramatta councillor, Shahadad Chowdhury pleaded with the community to help his mosque.

"Help us clean our backyard, to weed our backyard from all these problems."

Outside the mosque, Aaron, a convert of 17 years, who declined to give his second name, agreed with Mr Kadomi.

"He just said we need to work together and guide the youth," he said. "I think the boy was very foolish and had no right to do what he did. it was an act of evil. If you follow the teachings of the Koran you are not meant to do things like that."

Another worshipper insisted "Islam means peace. It is a religion of peace."

Hundreds of anti-Islamic protesters, however, are preparing to protest at the mosque on Friday afternoon, as their allies in Victoria geared up to do the same in Bendigo.

NSW Police condemned the unauthorised action and any planned acts of violence.

Race Discrimination Commissioner Tim Soutphommasane called for calm. He said the tragic shooting in Parramatta should not be used to justify racial or religious hatred.

"The community is right to be shocked by the murder of Curtis Cheng and to condemn such abhorrent violence," Dr Soutphommasane said. "However, no one should be taking the law into their own hands."

Cr Chowdhury echoed Dr Soutphommasane's words.

"We are suffering together and we will rise up together," he said. "We hope for a better future than this sad incident that happened last Friday."

Just 500 metres down the road outside the offices of the State Crime Command lay flowers put there by Muslims, Christians and the NSW police.

They wilted in the October heat, as bouquets began to swallow the memory of Curtis Cheng.