He was arrested on Tuesday after he exchanged messages and travelled to a Parramatta car park to meet with a person he thought was a gun seller. Tamim Khaja was once known for trying to be a "gangster". Credit:Facebook Mr Khaja was expected to be charged on Tuesday night with preparing to commit a terrorist attack and attempting to join the conflict in Syria. "This young person's life changed today," AFP Deputy Commissioner Neil Gaughan said. "When he made those decisions two weeks ago, he's now looking at life imprisonment." Fairfax Media understands a tip-off to the National Security Hotline last year first alerted police to his behaviour.

Mr Khaja was then investigated in July for allegedly preaching violent extremism in the playground of Epping Boys High School where he was a year 12 student. Tamim Khaja (centre) was arrested by counter-terrorism police. It's alleged he had attempted to leave the country three times to join the Islamic State terrorist group. Most recently, he was stopped at Sydney Airport in February trying to fly to Syria but his passport was cancelled. Mr Khaja then allegedly began planning an attack on home soil. It's understood he was weighing up his options for sites and had ruled some out after scouting them.

Deputy Police Commissioner Catherine Burn said police had been involved with the man for some time but he wasn't in a formal deradicalisation program. Friends told Fairfax Media that Mr Khaja used to hang out at a local skate park and portrayed himself as a "gangster" before becoming deeply religious. It's alleged Mr Khaja is close to imprisoned extremist Milad bin Ahmad-Shah al-Ahmadzai and his brother, Maywand Osman, who is also in custody on terrorism offences. Osman and al-Ahmadzai lived just a few kilometres away from Mr Khaja and also went to Epping Boys High. However, it's understood Mr Khaja's family, who are Australian citizens of Afghan heritage, are only moderately religious. One of Mr Khaja's older brothers is a commercial pilot, while another is a salesman whose public social media posts are more about international football and the Royal Easter Show than religion.

Mr Khaja left Epping Boys High School following the allegations he was trying to influence other students through a Muslim prayer group. The incident prompted the NSW government to conduct a state-wide audit of student prayer groups in schools. Some parents and students expressed their support for Mr Khaja at the time, saying he was a "blessing" to younger Muslim students. On Tuesday, a friend of Mr Khaja, Fatima Abdelrahim, said he was a "beautiful" boy who came from a good family. "His family are very clean, very intelligent. I've never seen them in trouble with the cops," she said.

Police spent hours searching the family's home and cars on Tuesday. Among the items seized from a car were a mobile phone, memory stick and green prayer mat. Ms Burn said it was the ninth terrorist attack police have thwarted and their strategy of pre-emptive, "disruptive" arrests was proving successful With David Wroe