The terrorist who killed a policeman in New South Wales is believed to have been part of an extremist group. Farhad Khalil Mohammad Jabar shot and killed police accountant Curtis Cheng, 58, in Parramatta, New South Wales on Friday. He was then himself shot and killed by police officers. Police are currently working on the theory that Jabar was not working alone, but was carrying out the instruction of other radicals. He was in communication with a known British radical linked to the Islamic State over the internet, according to counter-terrorism police. Police are investigated his known associates and the mosque he attended. They arrested a student from the same high school as Jabar and took him into custody this morning. The young man, who has not been named, posted messages in support of Jabar on Facebook just one hour after the attack, writing, "Serves you right I hope them lil piggies get shot." He later posted a video link to the press conference held by Police Commissioner Andrew Scipione and wrote, "Bahahja f*ck you motherf***er Yallah merryland police station is next hope they all burn in hell." Police say they spoke to him about the posts and took him into custody once he became threatening and abusive towards officers. Jabar is believed to have moved in the same circle as another 15-year-old who was arrested last year for yelling death threats at a Maronite College from a passing car while waving the Islamic State flag out of the window. A Facebook page labelling Jabar the "Hero of Parramatta" was set up in his memory, praising his terrorism. It used the Islamic State flag in its cover photo.