An Australian journalist who interviewed Ben Zygier shortly before he was detained by Israeli authorities says the Melbourne man "strenuously" denied being a spy.
But reporter Jason Koutsoukis says he suspected that his conversations with Mr Zygier, which began two months before the man's arrest in February 2010, were being monitored by Israeli intelligence.
Mr Zygier was found hanged in a supposedly suicide-proof cell on December 15, 2010.
Foreign Minister Bob Carr has ordered a review of the case, which has rocked the Australian and Israeli governments, after the Department of Foreign Affairs and Trade apparently gave him conflicting advice about who knew what.
Koutsoukis on Thursday told the ABC he interviewed Mr Zygier three or four times and that their last conversation may have been the same month Mr Zygier was arrested.
Koutsoukis said he had been tipped off in October 2009 by an Australian intelligence source who believed three dual national citizens - including Mr Zygier - had used Australian passports to spy for Israel in countries including Syria, Iran and Lebanon.
Koutsoukis said he interviewed Mr Zygier on a handful of occasions and that Mossad may have been aware the pair were in contact.
"He listened to what I had to say and it was, even to me, an outlandish story, what I was putting to him, and at the end of what I had to say he responded and denied it as strenuously as he could," Koutsoukis told the ABC.
"He was just incredulous."
The former Fairfax Media reporter said at first he found Mr Zygier "very convincing" but continued to interview him.
"It seemed to me that he was doing some kind of intelligence gathering but I couldn't be more certain than that," he said on Thursday.
He added that at the time, he thought it was possible his interactions with Mr Zygier were under Israeli surveillance.
"There were a couple of strange incidences which happened around my home in Jerusalem, which I didn't take seriously at the time, but in hindsight it is possible that they were monitoring our conversations," he said.