The FBI's Teenage Mole Inside WikiLeaks

June 30, 2013 — -- Sigurder "Siggi" Thordarson considers himself the man who blew the whistle on the whistleblowers.

He is the first known WikiLeaks volunteer to have flipped on the anti-secrecy organization by agreeing to inform on it and its controversial leader, Julian Assange, for the FBI two years ago, when Thordarson was just 18 years old.

In an interview with ABC News, Thordarson claimed that by the end, he handed over "pages of chat logs, thousands of pictures, videos, images, internal documents, et cetera, et cetera" about the organization, including the text of purported chats with Assange and high-profile WikiLeaks allies.

"The FBI obtained about one terabyte of data," he said, not to mention Thordarson's personal knowledge of the WikiLeaks organization members.

While it's unclear why exactly Thordarson flipped – he said the FBI just paid him $5,000 over several months -- or what the FBI did with all that information, he is unapologetic about what former WikiLeaks spokesperson and Icelandic lawmaker Birgitta Jonsdottir called a dangerous play with people's lives.

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The FBI declined to comment for this report and some details in Thordarson's story, which was first reported by WIRED.com Thursday, as well chat logs and emails provided to ABC News by Thordarson could not be independently verified. In response to the WIRED report, WikiLeaks tweeted that Thordarson's role was exaggerated and referred to a previous statement in which the organization called him "troubled young man" who "did manage several minor tasks for the organization as one of hundreds of volunteers all over the world." The rest of the report, Wikileaks said in a tweet to ABC News, "strongly accords with our previous statements."

"In light of the relentless ongoing persecution of U.S. authorities against WikiLeaks, it is not surprising that the FBI would try to abuse this troubled young man and involve him in some manner in the attempt to prosecute WikiLeaks staff," WikiLeaks said in a statement in February, without naming Thordarson. "There is strong indication that the FBI used a combination of coercion and payments to pressure the young man to cooperate."

But to hear Thordarson tell it, it was his idea from the start. It all began in August 2011 with an email.

"I contacted the U.S. Embassy in Iceland in an email which stated that I might have information about an ongoing criminal investigation going on in the United States," the now 20-year-old Icelander told ABC News.

Thordarson said someone from the embassy called him a few hours later. When Thordarson said he had information about the WikiLeaks investigation, the embassy official said there was no investigation.

"I told them that we both knew otherwise," Thordarson said.

The same day he was invited to the embassy and met with a security official there. At the end of the meeting he was told it would take days for anyone to get back to him, if they did at all. The next day, however, Thrordarson was summed back to the embassy and this time when he met with the security official, the official suggested they go "take a walk."

"And we walked downtown, in downtown Reykjavik, and circled probably every single building there, and then we ended up in a Reykjavik hotel where I was escorted inside a conference room," Thordarson said. "Then he said his goodbyes and there were those two individuals that identified themselves as federal agents."