Mehmet Biber in the backyard of his home in western Sydney. Credit:Fairfax Media On one of several Facebook profiles he has created then shut down in recent months, Mr Biber warned of more attacks like the shooting outside Parramatta last year by schoolboy Farhad Jabar. "Let the general public know that home ground attacks such as the likes of the one we seen at parramatta will start to become more frequent as the australian government sticks its hands deeper into the blood of the muslims via joint attacks on muslims overseas," he posted. After the Paris attacks in November, he posted: "f you attack Islam and Muslims for years on end indiscriminately then it's stupid and naive to think there wont be retaliation and consequences... just sayin". Mr Biber has written lengthy posts blaming the Australian government "for breeding homegrown extremism" and espousing the importance of hijrah – an Islamic concept of migration that has been hijacked by Islamic State to refer to the highly-meritorious journey to the group's new "caliphate".

Mehmet Biber. Credit:Facebook He said it is the most "undermined, feared, revered and belittled topic of our community leaders" and it was an obligation for Muslims in "lands of disbelief". "Fearing 'ohh but its so hard, ohh but i dont have enough money, ohh but its dangerous' is not an excuse," Mr Biber posted in September. Mehmet Biber with his Auburn soccer team. In another post he said, "unless you plan on leaving the land of the kuffaar for the land of the believers, then know that whatever may happen to you or your family by their hands, is on your neck, and you may be thrown into the hellfire onto your face."

His posts were "liked" by several young men arrested in counter-terrorism raids in Sydney, including a schoolmate of Jabar's who police believe linked the vulnerable 15-year-old to a network of extremists. A warning on the Facebook page of Mehmet Biber. Credit:Facebook Government and police officials have repeatedly spoken of the risk posed by the return of foreign fighters, who could possibly bring back dangerous expertise and ideologies. An AFP spokesman would not say whether Mr Biber had participated in any deradicalisation programs or been investigated thoroughly enough on his return. Funeral service for NSW Police employee Curtis Cheng, murdered outside Police Headquarters in Parramatta. Credit:James Brickwood

"Foreign fighters who have returned to Australia are considered by law enforcement and security agencies on a case-by-case basis," the spokesman said. "Returnees who are not subject to criminal charges are assessed for their level of risk to the community." It's believed Mr Biber has been living a quiet life in Sydney's west, playing soccer with an Auburn team, heading out on fishing trips and spending time with the family of his best friend, Caner Temel, who travelled with him to the Middle East and was killed in January 2014 while fighting with Islamic State. However, his recent Facebook posts will raise the eyebrows of authorities, who have decided not to charge Mr Biber under foreign incursion laws. In other posts, he shared a list of sheikhs who support Islamic State and shared photos of badly injured babies in Iraq, saying they were victims of coalition airstrikes and western governments are the "true terrorists".

Mr Biber allegedly left Australia with Mr Temel and another man on a flight to Singapore on July 1, 2013. They allegedly made their way to Turkey's Bab Al-Hawa border crossing with Tyler Casey, who was later killed during rebel in-fighting in Syria in January 2014, weeks before Mr Temel's death. When Mr Biber left Sydney unannounced, his family made a report to police and alerted Turkish authorities. The Sun-Herald has spoken with Biber several times. He said he did nothing wrong in the Middle East and returned home over two years ago, just weeks after he allegedly left. "If we spoke about anything incriminating then I'm sure the AFP would have pressed charges against me," Mr Biber said.

He said that his passport has been confiscated and if the government gave it back, he would voluntarily leave. Other sources cast doubt on his claim that he returned two years ago, saying he hadn't been located by December 2013, when western Sydney pensioner Hamdi Alqudsi was arrested and charged with facilitating for Mr Biber and six other men to travel to Syria to join Jabhat al-Nusra. Mr Biber also posted photos online in December 2013 of bombed-out buildings in Syria. After Mr Alqudsi's arrest, he posted that he was "a tourist not a terrorist". One security source said he was "extremely lucky" to have made it home and probably hadn't transitioned from Jabhat al-Nusra to Islamic State because Islamic State doesn't let fighters abandon the group without consequence.