15 yearold gunman Farhad Khalil Mohammad Jabar's final moments outside of the Parramatta Police Headquarters. Courtesy Seven News

POLICE Commissioner Andrew Scipione has vowed that “everything that needs to be done will be done,” to find how a 15-year-old schoolboy came to execute a much loved police accountant as he left work.

“There is no way you can describe the hurt inside that building and right across the NSW Police force at the moment,” he said outside Charles St headquarters this afternoon.

Mr Scipione was joined by Premier Mike Baird and Deputy Premier Troy Grant where they laid wreaths for slain Curtis Cheng.

They then went inside to meet the special constables that shot dead Farhad Khalil Mohammad Jabar in a brief gun battle.

News_Image_File: Minister for Justice and Police Troy Grant, NSW Premier Mike Baird and Police Commissioner Andrew Scipione reading some of the cards left for slain police finance worker Curtis Cheng. Picture: Jonathan NgNews_Image_File: NSW Premier Mike Baird, Police Commissioner Andrew Scipione and Minister for Justice and Police Troy Grant laying a wreath at Police Headquarter. Picture: Jonathan NgNews_Image_File: A tribute to Curtis Cheng outside the building. Picture: Jonathan Ng

Mr Baird said they were there to acknowledge “the bravery of some very special men”.

“We strongly believe they saved many lives,” he said.

Mr Baird said they were also there to show their support for the “police family”.

News_Image_File: With friends: Farhad (bottom left).

News_Image_File: Employees at Police Headquarters in Parramatta were emotional as they returned to work after the long weekend. Picture: Jonathan Ng

“We are here to try to help them know that everyone across this state is with them and they are not hurting alone.”

Mr Baird, Mr Scipione and Mr Grant also met Mr Cheng’s senior colleagues.

The floral tribute continues to grow outside the headquarters with people of different faiths praying and reflecting. Some make the sign of the cross, others pray and bow.

Earlier in the day a Buddhist monk stood and reflected.

Earlier this morning police arrested a student on his way to Arthur Phillip High School, the same school attended by the 15-year-old who shot a man dead at Parramatta’s police headquarters last week.

The arrested student had his belongings emptied on the footpath before being handcuffed and taken away in a police van.

Police said they spoke with the boy on his way to school this morning in relation to alleged posts on social media. He was arrested after allegedly threatening and intimidating officers and taken to Parramatta police station.

In a Facebook post on Friday, a little more than an hour after Farhad Jabar shot dead police worker Curtis Cheng outside the force’s Parramatta headquarters, he wrote: “Serves you right I hope them lil piggies get shot”.

He later posted a video of Police Commissioner Andrew Scipione’s press conference from the night of the shooting.

“Bahahja f*ck you motherf***er Yallah merryland police station is next hope they all burn in hell,” he wrote alongside it.

The boy describes himself as “A.W. A” or “Arab with attitude” and allegedly has a long history of uploading content taunting and mocking NSW Police.

News_Image_File: Officers surround the arrested youth outside school today. Photo: ABC

News_Image_File: Arrest ... The student is taken away by police this morning. Photo: ABC

News_Image_File: Another post shortly after Friday’s shooting.

He shared a photo of himself in front of two officers from the state’s mounted unit and wrote: “F*ck the police not a single f*ck was given that day FTP FTS”.

In a chilling post the day after Friday’s callous terror attack, one his friends wrote: “I knew it was going to happen, just didnt (sic) know when”.

According to the 17-year-old’s Facebook account, he travelled to Iran earlier this year.

In May he checked in to the resort-filled Kish Island and wrote: “Omg this place is heaven”

The Arthur Phillip High School student is also a member of the group Social Muslims Unite.

News_Image_File: Police secure the scene of the shooting / Picture: Phillip RogersNews_Image_File: Fears ... Teen shooter Farhad Jabar lies dead outside Parramatta police HQ

His arrest comes after The Daily Telegraph revealed police are working on the ­theory that teen terrorist Farhad Khalil Mohammad Jabar was acting on the orders of other radicals and was not a “lone wolf’’ killer.

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NSW counterterrorism ­officers are investigating who may have supplied the gun he used to carry out the murder of a civilian staffer at Parramatta police headquarters on Friday afternoon.

Counter terrorism police today revealed Jabar had been communicating online with a British Jihadist with known links to IS, the Australian reported.

“The possibility the teenager was used by extremists is a strong line of inquiry,’’ a senior officer involved in the operation told The Daily Telegraph.

News_Image_File: Grim following ... Cartoon in today’s Daily Telegraph

“That includes searching his computers, electronic devices and who he was in contact with on the days leading up to the shooting and on the day itself.’’

The development comes amid reports in The Australian today that investigators have linked Jabar to a known British radical associated with terror group Islamic State, and that the pair had been communicating via the internet.

They have also established the schoolboy was at his home last Friday morning before he went to Parramatta mosque in the afternoon, where he ­listened to sermons by two imams.

“What was said in those sermons and who he may have met at the mosque are all now being investigated,” the senior officer said.

“There are hours of video and ­recordings to go through.’’

Jabar’s school friends and ­religious associates will all be ­interviewed in the next few days.

News_Image_File: Colleagues of Curtis Cheng outside the NSW Police Headquarters yesterday. Picture: Jonathan NgNews_Image_File: Grieving ... Colleagues of Curtis Cheng outside Parramatta police HQ yesterday, Picture: Jonathan Ng

Police will also go through CCTV footage of the possible routes Jabar used as he walked from the mosque in Marsden St, Parramatta, carrying a backpack, to the police headquarters on Charles St to see if he met anyone after ­visiting the mosque.

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Detectives are confident a backpack recovered on Friday evening near the scene was used to carry the .38 silver Smith and Wesson gun Jabar used when he shot police employee Curtis Cheung in the back of the head about 4.30pm.

It has also been established that he changed into a black robe at the mosque and then walked to the police station, dumping his street clothes in a garbage bin along the way.

Inside the backpack which Jabar dumped 300m from the fatal shooting was material ­bearing the name of a western Sydney Islamic book store.

Police are not releasing the name of the store or whether they have interviewed staff but have revealed Arabic writings found at the home of the killer and his family are being ­accessed to see if they are ­connected to the act of terror.

News_Image_File: Farhad Khalil Mohammad Jabar taunts police. News_Image_File: An officer exchanges fire

The family are said to be ­naturalised Australians, with the ­father and brother both working to provide for the family. The parents and brother have all been interviewed several times by police.

Jabar’s sister, Shadi, a student aged in her 20s, lived in the ­family’s flat in Parramatta until she left the country the day ­before the terrorist attack.

“Federal police are now looking into her movements. It ­appears she flew to Singapore then onto Istanbul. Why she was going has not been established,’’ the officer said.

Police are calling for the community to unite in the wake of the tragedy and are scrutinising online chat rooms fearing it could ignite some form of revenge attack.

“What we can’t allow to ­happen is to let that tragedy divide us, to split us apart,” Deputy Commissioner Nick Kaldas said.

More than 100 police are now involved in the investigation.