Mohammed Ali Baryalei has not been charged, and is likely still in Turkey, the Australian Broadcasting Corp. reported.
Baryalei left Australia in April last year. Australian police intercepted one of his phone calls two months later, and the conversation indicated he had been to a battle where people had been killed and injured.
He allegedly worked with Hamdi al-Qudsi, a man from Sydney who was arrested in December for sending six young Australians to fight in Syria.
Two of those fighters, Caner Temel and Yusuf Ali, were killed last week.
Ali's young wife was also killed, the ABC reported.