The teenager, whose name is suppressed, was found with a photograph performing what is thought to be an ISIS salute.

His drawings in custody include a plane flying into an Australian Federal Police building and a person preparing to behead another, along with the words "Islamic State" and "God is great" in Arabic.

While there is no evidence the 19-year-old has taken part in any terrorist acts, he claims to have tried to make online contact with Islamic extremists.

Despite his young age, the teenager has spent all but eight months in custody over the past six years.

His last jail term expired in April.

His priors include multiple armed robberies, pistol possession, property offences and more.

He started using drugs aged about 13 or 14, particularly ice, and is on anti-psychotic medication for mental health issues.

His earliest terrorist related incident occurred in November 2015 while watching coverage of the Paris terrorist attacks, which killed 138 people through suicide bombings.

The boy, who was in a detention centre, said he wanted to be part of Islamic State.

The most recent incident occurred while in custody in June 2017, when he wrote ISIS inspired graffiti on a chalk board.

He wrote "behead those who dog the brothers" and "f--- the infidels, behead them all" amongst other comments.

The teenager told authorities last November he was still following the Muslim faith and was praying five times a day.

He had said he wanted to live under sharia law.

The NSW Supreme Court recently approved an interim request to closely monitor the boy, which will allow his computers and other devices to be checked at any time, for authorities to visit his home at any time, and for other restrictions to be imposed.

Authorities will be able to use monitoring equipment, and can ban him from changing address and associating with certain people.