The Sydney barrister representing the relatives of Islamic State fighter Khaled Sharrouf says he thinks the man may still be alive and living in Iraq.
"If I was a betting man I'd say he's alive," barrister Charles Waterstreet said on Sunday.
"I think he's probably in Iraq and I think he's immobilised...incapacitated in some way."
In June last year it was widely reported that Sharrouf and another IS fighter from Sydney, Mohammed Elomar, had been killed in an American drone strike.
But doubts have now emerged over the veracity of those claims.
News Ltd reports that law enforcement officials have discovered apparent attempts by Sharrouf to contact people in Sydney, including making death threats.
Mr Waterstreet is helping Sharrouf's stepdaughter in her attempt to have the terrorists's children brought back to Australia following the death of their mother, Tara Nettleton.
He said Sharrouf was well versed in the art of deception, suggesting that the Sydney man had fooled a Supreme Court judge into thinking he had a severe mental illness when he was charged with terrorism offences in 2005.
"Someone who was bright enough to fool a judge like Justice Anthony Whealy into a light sentence is not to be underestimated," he said.
Foreign Minister Julie Bishop would not confirm whether Sharrouf is alive or dead and said the extremist's reckless actions have shown disregard for the welfare of his children.
"The Australian government is unable to confirm the current status of convicted terrorist Khaled Sharrouf, although it is disturbing to read reports that someone claiming to be Mr Sharrouf is threatening people in Australia," Ms Bishop said on Sunday.
"Mr Sharrouf joined the violent terrorist organisation Da'esh in Syria and Iraq, and recklessly brought his wife and children into a conflict zone controlled by the group.
"His wife is reported to have died recently, which raises serious concerns about the welfare of his children and grandchild."
It was reported on Thursday that Sharrouf's wife, Tara Nettleton, died late last year from complications due appendicitis.