Adam Brookman, 39, was arrested at Sydney International Airport on Friday night on a Victoria state warrant relating to his alleged involvement in the conflict in Syria, Australian Federal Police said yesterday.
He is the first Australian involved with Isis known to have returned home since the Sunni fighters swept into western Iraq in June last year and declared the establishment of a caliphate, Monash University terrorism expert Greg Barton said.
"He's certainly the first Australian to come back from Isis-controlled territory having lived and worked among Isis," Barton said. "Culpability is the nub of the issue here."
But none has been charged because of a lack of proof.
Brookman appeared from a police cell by video link in the Parramatta Bail Court yesterday, where a magistrate granted an application by the Melbourne Joint Counter Terrorism Team to extradite him to his hometown of Melbourne in Victoria.
He is to appear in a Melbourne court no later than tomorrow morning on two charges that each carries a maximum of 25 years in prison.
Court documents show both charges allege that Brookman knowingly provided support to Isis by undertaking guard duty and reconnaissance for the militants. That support would allegedly help the group "prepare or foster" a terrorist act.
Brookman did not speak during his brief appearance.
He surrendered to Turkish officials in Turkey on Tuesday and voluntarily flew back to Australia with a police escort.
Brookman, a Muslim convert and father of five children who live in Melbourne, told Fairfax Media in May that he went to Syria last year to do humanitarian work for civilians caught in the war.
He said he was innocent of any crime and was forced to join Isis militants after being injured in an airstrike and taken to a hospital controlled by the group at al-Bab in Aleppo province.
"After I recovered, they wouldn't let me leave," he told Fairfax.
He won the militants' trust by working as a medic and was able to escape to Turkey in December, he said.
Brookman told Fairfax that he opposed the violent and extreme actions of the militants, including the beheading of their captives.
"Of course there will be an investigation. That is fine. Hopefully things don't look that bad," Brookman told Fairfax.

