And police say they have a long way to go until they have a full picture of who was the 15-year-old Parramatta gunman Farhad Khalil Mohammad Jabar and what motivated him.

Police said the teenager was of Iraqi-Kurdish background and born in Iran. He had been living with family at a North Parramatta apartment block and attending Arthur Phillip High School just 300 metres from where he would carry out the attack.

Fairfax Media has been told the teen visited nearby Parramatta mosque, where he changed into a flowing black shirt and black trousers prior to travelling to the other end of Parramatta's CBD where he opened fire.

His Twitter account, untouched since 2013, highlights his young age, with tweets about reality talent show The Voice and him wearing a US basketball jersey.

"Team is [sic] Ricky is the best and he is the best coach," he posted in April 2013.

His Facebook page shows a young-faced boy mucking around with another young mate. He had not posted publicly on the page since 2010.

A police source said his name was not one they had heard before Friday. He was not contained in any intelligence reports and he did not appear to have any links to those targeted by police in previous counter terrorism raids.

"We don't know a lot about this guy," the source said. "He hasn't been one of our targets. Before yesterday we didn't even know him let alone see him as a threat."

Police on Saturday were talking with his family who were also trying to shed light on what might have happened.

"They are contributing to finding out what's happened," the source said. "What we have got to do is go back and look through everything."

No one answered the door at the family home in North Parramatta on Saturday but neighbours confirmed detectives had arrived at the home the night before.

The family live in a large unit complex on a quiet leafy street, a few minutes drive from the NSW Police headquarters in Parramatta.