"They asked me first for proof of who I was so I provided them with identification… Then they asked me what I did for the organization, I explained what I did," Thordarson said.
Thordarson said he had joined WikiLeaks in February 2010 as one of many volunteers but was elevated to a key position after several staff members left the group in September of that year. He was assigned to run the organization's IRC chat room, considered a gateway into the organization for volunteers and potential sources alike.
Jonsdottir, who was a WikiLeaks volunteer herself when Thordarson joined the organization, said she tried to warn Assange about Thordarson.
"I recognized quite early on there was something not quite right about his extraordinary stories," said Jonsdottir, who is no longer affiliated with the organization.
Assange apparently did not heed her warning and Thordarson said he was given more responsibility in the organization. A little less than a year later, Thordarson said he decided to turn on WikiLeaks by contacting the U.S. Embassy.
Over the next several months, Thordarson said he exchanged emails with an FBI handler and met with agents a handful of times in Europe and once in Washington, D.C. He said he gave them with hard drives of packed with inside information, but declined when the FBI agents allegedly asked him to wear a watch with a recording device in it to tape Assange. He also volunteered to appear before the Icelandic parliament in a confidential session, which Jonsdittor attended. Thordarson provided ABC News with copies of the alleged emails and travel documents to bolster his claims.
In the emails with the purported FBI handler, Thordarson is alternatively thanked and sporadically ignored. Several times Thordarson politely asks about money he believed he was owed by the FBI. He later told ABC News the $5,000 he took from the U.S. government was not a payoff, but just meant to cover for the work he missed during their meetings.
In the interview with ABC News, Thordarson said his decision to turn on WikiLeaks came because he grew to believe Assange was "guilty of something, but crimes I'm not so sure."
Later, Thordarson clarified in an email that he didn't want to "participate in illegal hacking against government/corporations just so that WikiLeaks could have something to leak." But as WIRED reported, Thordarson was the one that once asked Lulzsec, a WikiLeaks affiliated hacktivist group, to hack the Iceland government's website.
Jonsdittor said she believes he did it because he was "terrified" of being prosecuted in the U.S. She said she's concerned about what Thordarson may have told the FBI about her former associates, worried he may have lied to the FBI as well.
"He was feeding information to the FBI about my friends and I don't know what he was saying," she said. "I believe he has some psychological issues, and that he needs to seek legal help before this media narrative spins out of control."
The U.S. government has not announced any indictment against Assange, who is living in the Ecuadorian Embassy in London to avoid extradition to Sweden to face sexual assault charges, but his attorney, Michael Ratner, told The Huffington Post earlier this month that he believes there is "more likely than not" a sealed indictment in the U.S. against the WikiLeaks founder already.
Thordarson's life as a double agent of sorts ended in July 2012 when he was booted from WikiLeaks for allegedly selling WikiLeaks merchandise online and pocketing the profits – some $50,000, according to WikiLeaks. Thordarson said it was all a misunderstanding. He said he is also facing criminal charges unrelated to his WikiLeaks work for what he called "financial crimes and tax evasion," to which he said he plans to plead guilty.
He said he chose to tell his story to the media now because he believed his role as a snitch was starting to slip out and "instead of people speculating, I decided now recently to just tell the story."
Officials at the U.S. Embassy in Iceland did not immediately respond to an off-hours call and email Saturday.