Jack Roche, on trial for plotting to blow up Israel's embassy in Australia, has said he went along with the plot because he feared for his life.
Mr Roche told the court he had agreed to conduct surveillance of the embassy for al-Qaeda and Asian militant group Jemaah Islamiah (JI).
But he said the surveillance was never explained to him, and he was innocent of the terrorism charges he faces.
"I was in a situation and I couldn't stop it," he said.
"You just don't walk away from these kinds of people," Mr Roche
told Perth District Court during his second day on the witness stand.
50-year-old Muslim convert born in England as Paul Holland
Admits being a former JI member
Denies charges of attempted terrorism
Insists Abu Bakar Ba'asyir headed militant group JI
Mr Roche, a 50-year-old Islamic convert, went to Afghanistan in 2000, where he received explosives training and met Osama Bin Laden.
Upon his return to Australia he went to Canberra and filmed outside the Israeli embassy in June 2000, and the resulting footage was shown to the courtroom
He said he had to be seen to be doing his task, in case
someone from a militant group was watching.
He also said he tried to cause tension between twin brothers Abdulrahman and
Abdulrahim Ayub - widely believed to have led Jemaah
Islamiah in Australia - and Hambali, the region's operations chief.
He said he thought creating problems within the group might prevent the attack from going ahead.
In taped evidence to court on Wednesday, Mr Roche said Indonesian cleric Abu Bakar Ba'asyir - who he claims headed JI - eventually told him to halt his plans following such disagreements.
Mr Roche also said that, although he met senior militant leaders in Afghanistan, it was only when he logged onto a website showing the US FBI's most wanted fugitives that he learned the identities of some of the people he had seen.
"I was shocked. I was really taken aback," he said. "I was thinking 'this is too much - this is very, very deep'."
Jack Roche was arrested during raids in Australia in the aftermath of the Bali bombings in late 2002.
He told police he joined the Australian branch of JI in 1996.
Mr Roche said he left following disagreements with the Ayub brothers in mid-2000, around the time prosecutors allege he was plotting to bomb the Israeli embassy.
He said he became disillusioned, and went to the US consulate in Sydney to tell them what he knew.
But the embassy directed him to the
Australian Security Intelligence Organisation (ASIO), where "nobody seemed particularly interested in what was going on," Mr Roche said.
Jack Roche was born in the UK, but has been living in Perth in Western Australia for several years. He converted to Islam more than a decade ago.
His lawyer has insisted he is innocent, but he faces a maximum sentence of 45 years in prison if convicted of attempted terrorism.
The trial continues.