Sigurdur Thordarson and Julian Assange in England in 2011. Note the ankle bracelet that Assange is wearing. Credit:Courtesy Sigurdur Thordarson Thordarson, who first outed himself as an informant in a Wired story in June, provided me with access to a pseudonymous email account that he says was created for him by the FBI. He also produced documents and travel records for trips to Denmark and the United States that he says were organised and paid for by the bureau. The FBI declined to comment on Thordarson's role as an informant or the content of the emails its agents are alleged to have sent him. In a statement, it said that it was "not able to discuss investigative tools and techniques, nor comment on ongoing investigations." But emails sent by alleged FBI agents to Thordarson, which left a digital trail leading back to computers located within the United States, appear to shine a light on the extent of the bureau's efforts to aggressively investigate WikiLeaks following the whistle-blower website's publication of classified US military and State Department files in 2010.

Flipped: Hector Monsegur, aka Sabu, the loudmouth figurehead of LulzSec. Late last month, Army intelligence analyst Bradley Manning was convicted on counts of espionage, theft and computer fraud for passing the group the secrets. During the Manning trial, military prosecutors portrayed Assange as an "information anarchist," and now it seems increasingly possible that the US government may next go after the 42-year-old Australian for his role in obtaining and publishing the documents. For the past 14 months, Assange has been living in Ecuador's London Embassy after being granted political asylum by the country over fears that, if he is sent to Sweden to face sexual offence allegations, he will be detained and subsequently extradited to the United States. Meanwhile, for more than two years, prosecutors have been quietly conducting a sweeping investigation into WikiLeaks that remains active today. The FBI's files in the Manning case number more than 42,000 pages, according to statements made during the soldier's pretrial hearings, and that stack of proverbial paper likely continues to grow.

Thordarson says he was instructed to build relationships with people close to WikiLeaks in order to gather information for the feds. Thordarson's story offers a unique insight into the politically-charged probe: Information he has provided appears to show that there was internal tension within the FBI over a controversial attempt to infiltrate and gather intelligence on the whistle-blower group. Thordarson gave the FBI a large amount of data on WikiLeaks, including private chat message logs, photographs, and contact details of volunteers, activists, and journalists affiliated with the organisation. Thordarson alleges that the FBI even asked him to covertly record conversations with Assange in a bid to tie him to a criminal hacking conspiracy. The feds pulled back only after becoming concerned that the Australian was close to discovering the spy effort. A thirst for adventure

It was 2010 when the saga began in Reykjavik, Iceland. Thordarson, then just 17, says that before his first encounter with Assange, he knew little about the man beyond a few YouTube videos he'd watched about WikiLeaks. But he went to hear Assange speak at a conference hosted by an Icelandic university, and the teenager was impressed. After the event, a journalist Thordarson knew introduced him to Assange, and the pair struck up a relationship that led to Thordarson doing some volunteer work for the organisation. Before long, he was on the edges of WikiLeaks' small, tight-knit inner circle. At that time, the group was sitting on the explosive files it had received from Manning that included a video showing a US helicopter attack that resulted in the deaths of 12 civilians, among them two employees of the Reuters news agency. Thordarson, a blond-haired stocky figure with a baby face, was present while WikiLeaks staff and volunteers in Reykjavik were preparing the video for publication. When it was published by WikiLeaks in April 2010, under the name Collateral Murder, it catapulted the organisation into the international spotlight and provoked an angry response from government officials in Washington. The then-teenager, known as "Siggi" to his friends, was around at the height of that backlash. He was given administrative privileges to moderate an internet chat room run by WikiLeaks. And when Assange relocated from Iceland to England, Thordarson came to visit. He even accompanied the WikiLeaks founder to court appearances in London as he fought extradition to Sweden over allegations of sexual assault.

Thordarson looked up to Assange, viewing him as a friend. The WikiLeaks chief, he says, treated him well – helping him find a lawyer in 2010, not long after the pair had met, when he says he was wrongly accused by Icelandic police of breaking into a business premises. But signs that Thordarson had a proclivity for brushes with the law did not appear to trigger alarm bells early on at WikiLeaks – though perhaps they should have, because he was certainly not any ordinary volunteer. Unlike many drawn to WikiLeaks, Thordarson does not seem to have been principally motivated by a passion for the cause of transparency or by the desire to expose government wrongdoing. Instead, he was on the hunt for excitement and got a thrill out of being close to people publishing secret government documents. As a child, Thordarson led a fairly normal middle-class life in Reykjavik, enjoying social studies and chemistry at school. His father worked as a sales manager at a painting firm, and his mother ran a hair salon. But as he entered his teenage years, he says, he began to feel that he could not connect with others in his peer group. He went to university to study computer science and psychology – but claims he was suspended after hacking into a computer system.

By mid-2011, Thordarson's thirst for adventure, combined with his interest in hacking, would irreversibly complicate his relationship with WikiLeaks. In June of that year, the Anonymous-linked hacker group LulzSec brought down the website of the CIA. Thordarson says that he and other WikiLeaks staff were amused by the incident, and he decided to reach out to the hackers to establish contact. Thordarson claims that, using the aliases "Q" and "Penguin X," he set up a line of communication between WikiLeaks and LulzSec. During the series of exchanges that followed, Thordarson says he "suggested" that his group wanted assistance to find evidence of anti-WikiLeaks sentiment within the Icelandic government's Ministry of Finance, which had thwarted an attempt by DataCell, a company that processes WikiLeaks donations, to purchase a large new data center in Reykjavik. (In early 2011, DataCell's founder questioned whether the Icelandic government had deliberately prevented the deal because it was "afraid of letting WikiLeaks here into the country.") "That was basically the first assignment WikiLeaks gave to LulzSec," Thordarson alleges, "to breach the Icelandic government infrastructure."

Thordarson admits that he initiated the contact with the hackers, though he claims it was approved by Assange. It is unclear, however, whether WikiLeaks staff were fully aware of his correspondence with LulzSec and the "assignment" that he says he handed to them. WikiLeaks spokesman Kristinn Hrafnsson told me he believed that if Thordarson had any contact with LulzSec, it was as a rogue operative and that it was "highly unlikely" any other WikiLeaks staff, including Assange, knew what he was engaged in. Thordarson is a dishonest character, Hrafnsson said, who is trying to inflate the role he played as a volunteer. Either way, in this case, the exchange Thordarson describes does appear to have taken place. It has since been independently corroborated in part by authorities in Iceland and was first reported – from the perspective of the hackers – in a 2012 book by Parmy Olsen, We Are Anonymous. I have also seen chat logs and emails from 2011 that appear to back up Thordarson's assertion that he was communicating with the hackers, which has significant ramifications. By claiming that he effectively solicited LulzSec to break into government computers, Thordarson has implicated himself in a potential international criminal conspiracy, leaving WikiLeaks open to the allegation that it, too, was somehow involved.

Dramatic twist But the full facts about the incident remain murky – not least because there is another dramatic twist to the tale. What Thordarson did not know at the time was that Sabu, the loudmouth figurehead of LulzSec and one of the hackers he was communicating with, was in fact working as an FBI informant – and the online chat about hacking Icelandic government infrastructure was apparently being monitored by the feds. About four days later, the FBI contacted Icelandic authorities to warn them about an "imminent" hacking attack, according to Iceland's state prosecutor, and this prompted Icelandic police to travel to the United States to discuss the matter. (Sabu, it later turned out, was a then-28-year-old hacker from New York named Hector Monsegur. The FBI reportedly tracked him to his Lower East Side apartment in early June 2011 and managed to "flip" him, because he was the guardian of two young children and desperate to stay out of jail.)

Thordarson says LulzSec never gave WikiLeaks any information about Icelandic government corruption, but hackers close to the group did hand over a confidential Icelandic state police document related to the security of the US Embassy in Reykjavik. He also claims that hackers affiliated with LulzSec and Anonymous turned over documents from a bank in Mexico, files from BP, and emails hacked from the Syrian government and the security think tank Stratfor, among others. Between February 2012 and July 2012, a large cache of Syrian government and Stratfor emails were published by WikiLeaks under the names the "Syria Files" and the "Global Intelligence Files." (As a matter of policy, WikiLeaks does not comment on how its releases are sourced.) Being at the centre of the action had given Thordarson the adrenaline rush he was looking for. But the contact with LulzSec, which he had initiated, made him feel like he had gone too far. He was worried that in maintaining contact with the hackers, he was "breaking quite a lot of laws." Meanwhile, news reports were saying that the U.S. government was already investigating WikiLeaks for its publication of classified documents, including the Collateral Murder video, diplomatic cables, and military war logs from Afghanistan and Iraq.

And just as Thordarson was getting anxious about the high-stakes international affairs he had become entangled with, he also seems to have become bored with WikiLeaks – and he now admits he wanted to embark on a new adventure. It was then that, at about 3:30am on August 23, 2011, Thordarson sat down at his computer at home in Kópavogur and typed out a message to the US Embassy in Reykjavik. He decided he wanted to become an informant – and, unlike Sabu, he was ready to do so without any threats hanging over his head. From: [redacted]@live.com To: reykjavikdatt@state.gov Subject: Regarding an Ongoing Criminal investigation in the United States. Date: Tue, 23 Aug 2011 03:33:39 +0000 After a quick search on the internet i have yet not been able to find a reliable contact form to establish a meeting with a person regarding an on going criminal investigation. The nature of the investigation is not something that i desire to speak over an email conversation. The nature of the intel that can be brought to light in that investigation will not be spoken over email conversation. I here by request a meeting at the U.S Embassy in Iceland, or any other place. I am an Icelandic citizen. I can be contacted via this email address Or Via Phone 00xxx-xxxxxxx I request also that this email will be considered confidential. Later that day, Thordarson received a phone call. On the other end, he says, was the security chief at the US Embassy in Reykjavik. The man asked what exactly the email was concerning, and Thordarson told him it was about the US government's ongoing investigation into WikiLeaks. He says the security chief denied the existence of any such investigation, but nevertheless asked Thordarson to come to the embassy to meet him. Thordarson agreed. And that afternoon, he turned up at the door of the Reykjavik embassy, explaining briefly that he wanted to share information about WikiLeaks. To prove he wasn't bluffing, he showed staff a photocopy of Julian Assange's passport that he had obtained.

He says he was told not to expect any further contact for at least a week, if at all. But less than 24 hours later, Thordarson's phone rang again. He was asked if he could come back to the embassy for another meeting. This time, it was serious. Unlike the more casual first meeting, he was told to hand over any electronic devices and take off his watch. He was then escorted by the embassy security chief on a walk around Reykjavik, circling the city center a number of times to ensure they were not being followed. Then he was ushered into a conference room in the four-star Hotel Reykjavik Centrum, where, he says, two men were waiting for him. They spoke with American accents and displayed FBI credentials. Iceland's state prosecutor has acknowledged that this meeting took place, confirming in a document published earlier this year that a handful of FBI agents and federal prosecutors were authorised to jet into the country after an Icelandic citizen contacted the US Embassy in Reykjavik. The US Embassy did not respond to a request for comment. For a brief moment, Thordarson became nervous. "The only thing that went through my mind was: 'What the [expletive] am I doing?' " he recalls. But the feeling of doubt didn't last long, and soon he was embracing the whole experience – almost as if he believed he was starring in his own personal spy thriller. The FBI, he says, asked him a range of questions to "verify that I wasn't full of [expletive]." At one point, he was asked what he knew about LulzSec, and he described the online conversations he had been having with Sabu.

The LulzSec connection Thordarson did not know it at the time, but the FBI had presumably been monitoring those chats – as an informant, Sabu had been issued a government laptop, and his online activity was reportedly under surveillance 24/7. Indeed, the bureau had met with Icelandic authorities two months earlier to warn about a potential hacking attack on Icelandic infrastructure – just days after Thordarson says he gave LulzSec the "assignment" to hack Icelandic government computers. Thordarson's detailed knowledge of the Sabu chats – and his participation in them – apparently convinced the agents. For about the next four consecutive days, they met with him, Thordarson says, each time at a different hotel in Reykjavik. They asked about people connected to WikiLeaks and quizzed him about what Assange was doing at Ellingham Hall, the remote residence in England's countryside where the WikiLeaks founder was living at the time while on bail and fighting extradition to Sweden.

Thordarson says the agents also wanted information about WikiLeaks' technical and physical security and the locations of WikiLeaks' servers; they asked him, too, for names of individuals linked to WikiLeaks who might be open to becoming informants if approached by the FBI. However, by August 30, 2011, several days after the FBI entered Iceland, the Icelandic government had become unsettled about the presence of US authorities. Then-Interior Minister Ögmundur Jónasson told me that Icelandic authorities initially believed the FBI agents had come to the country to continue their investigation into the impending LulzSec hacking attack on Icelandic government computers. But once it became clear that the FBI agents were in fact engaged in a broader swoop to gather intelligence on WikiLeaks, according to Jónasson, the agents were asked to immediately remove themselves from the country. "I think it was a question of trying to frame Julian Assange," Jónasson says, recalling the debacle. "And they wanted Icelandic authorities to help them with that." WikiLeaks ally DataCell had just months earlier accused the Icelandic government of working against the whistle-blower group, but by booting the FBI out of the country, the Interior Ministry had radically undermined that theory. Its decision, in fact, was a stark illustration of how WikiLeaks has continued to maintain a strong support base in Iceland since 2009, when it exposed controversial loan payments made by Kaupthing, the bank at the heart of the Icelandic financial crisis.

As a result, the FBI could not meet with Thordarson in Iceland again. Instead, he says, the FBI held further meetings with him in Denmark (three times) and brought him to the United States (once) to continue discussions about WikiLeaks. Through this period, Thordarson says the bureau paid him about $US5000 in total to cover his expenses and to make up for loss of earnings. Thordarson maintained contact with WikiLeaks, but he was secretly sending information back to the FBI. Once, he says, he told the agents that he was planning a visit to see Assange at Ellingham Hall. Eager to take advantage of the trip, they asked him to wear a recording device and make copies of data stored on laptops used by WikiLeaks staff. He alleges that the FBI wanted him to get Assange to "say something incriminating about LulzSec." But he declined to wear a recording device and told his handlers that covertly copying data from computers wouldn't be feasible because "people literally sleep with their laptops at Ellingham." Thordarson felt that wearing a wire in an attempt to secretly implicate Assange in LulzSec's illegal hacking activities was a step too far, but he was happy to engage in equally dubious intelligence-gathering activities. He maintained contact with LulzSec and passed transcripts of his conversations with the hacker Sabu back to the FBI, his emails show. What Thordarson did not know at the time was that the FBI already knew about the chats – because, of course, it had recruited Sabu as an informant, too.

In one notable online exchange in November 2011, Sabu told Thordarson that LulzSec had breached Syrian government computers. He showed off snippets of hacked emails to Thordarson, saying he wanted to pass a trove of data to WikiLeaks. Later in the same conversation, Thordarson quizzed Sabu about a plan to "recruit" him for WikiLeaks. Neither of the two men appear to have realised that they were both independently acting as informants for the FBI. "We ended up [inside] a certain government's central mail server and got some [expletive] massive leaks coming out," Sabu says in the chat. "You gents sure you're not wanting to do anymore leaks?" "Did J say anything about recruiting you permanently?" Thordarson fires back a few minutes later, in reference to Assange. "Well he emailed me once but we didn't get to talk," Sabu says. "Guess he's been busy/careful or whatever. But let him know we have intercepted 92GB of mails from .gov.sy [the Syrian government] so this can be one of the biggest leaks in history." When Sabu was outed as an informant in an explosive Fox News story in March 2012, it made sense to Thordarson. He says he found it strange that the FBI never seemed interested in the information he told them he had about the hacker, who was a hugely prominent figure at the helm of a group that had claimed responsibility for attacking US government websites and multinational corporations, including Sony and News International.

Handing over WikiLeaks data What the FBI agents wanted from Thordarson, it seems clear, was information that they could not get from any other source – information about the inner workings of WikiLeaks. Before his penultimate meeting with US authorities, in early February 2012, Thordarson says he was instructed to build relationships with people close to WikiLeaks in order to gather information for the feds. He received an email from his alleged handler – who used the alias "Roger Bossard" – in an account set up for him under the fake name "Ibrahim Mohammad." The message encouraged Thordarson to "chat with those people we discussed on the phone" in order to "get a head start before our meet." A few weeks later, he was flown out to Washington, DC, and says he was put up in a Marriott hotel in Arlington, Virginia, near the location of a grand jury that has been collecting evidence about WikiLeaks since at least early 2011 as part of a criminal investigation into the whistle-blower organisation.

At meetings in a conference room of the hotel, he was asked about a host of individuals who had at one time volunteered or worked for WikiLeaks in some capacity, including Icelandic parliamentarian Birgitta Jónsdóttir; eminent computer security expert Jacob Appelbaum; and Guardian reporter James Ball, a former WikiLeaks staffer. "They wanted to know literally everything there was to know about these people," Thordarson alleges. He says he "mostly gave them information that was general knowledge." But he admits that he turned over some email addresses, details about instant messenger accounts, and phone numbers. This information is useful to the authorities because they can use it to order surveillance of targeted suspects' phone or email accounts. Since 2010, several individuals connected to WikiLeaks have had emails and other communications monitored as part of the FBI's investigation. By the end of the meeting in Washington, the US government had already gleaned a large amount of information about WikiLeaks from Thordarson. Its biggest haul of intelligence, however, was yet to come. On March 18, 2012, Thordarson says he met with the FBI for what would be the final time, in Aarhus, Denmark. Prior to the meeting, he exchanged emails with his alleged handler, agreeing that he would come equipped with hard drives packed with chat logs, photographs, and other data related to WikiLeaks.

According to a Justice Department receipt Thordarson says was provided by the FBI, he turned over eight hard drives in total containing of about 1 terabyte of data, which is the equivalent of about 1000 copies of the Encyclopedia Britannica. (The Ministry of Justice in Denmark refused to comment on whether it authorised FBI agents to enter the country to meet with Thordarson, saying that it could not discuss "specific cases.") Once the agents obtained the hard drives and received the passwords to access them, Thordarson's emails suggest, they stopped responding regularly to his messages and rebuffed his attempts to set up another meeting. (Apparently, Thordarson's thirst for adventure hadn't yet been quenched.) They continued to encourage him to send data on WikiLeaks to a P.O. box at a UPS store in Arlington, a short drive from Justice Department and FBI headquarters, but they pulled back, apparently concerned that their cover could soon be blown. "Understand J has your laptop," an alleged agent wrote to Thordarson shortly after the final Denmark meeting, referencing Assange. "Is there anything on it about our relationship?" There were also signs that internal conflict was developing within the FBI over the infiltration of WikiLeaks, a controversial tactic not least because WikiLeaks is a publisher and press freedom groups have condemned from the outset the government's investigation into Assange and his colleagues.

In early 2012, after a period of not responding to Thordarson's emails, his alleged FBI handler wrote that there had been "bureaucratic issues beyond my control that prevented me from maintaining contact," adding that "our relationship has been problematic for some others. This is not an ordinary case. But those were not my issues and I have been diligently trying to work out those issues so we can continue our relationship." Thordarson, too, was having problems. He had become embroiled in a serious dispute with WikiLeaks about money in late 2011, which created friction between him, Assange, and WikiLeaks, ultimately resulting in him being dismissed from his volunteer role and perhaps even fueling his desire to continue informing on the group. Thordarson was accused of embezzling about $US50,000 from a merchandise store that he had helped set up to raise funds. He admits that he took some of the money but denies stealing it, saying he used the funds to cover expenses he was owed by WikiLeaks. The matter is currently being investigated by police in Iceland. In February, Iceland's state prosecutor published a detailed timeline about the FBI's visit to the country in 2011. The information shed light on the circumstances surrounding how US authorities were asked to leave because of their attempt to gather intelligence on WikiLeaks. The same month, Thordarson was called to appear at a closed-door meeting with Icelandic parliamentarians to discuss the extent of his dealings with the FBI, which led to him being named in the Icelandic press as the person who had prompted the FBI to fly to the country in August 2011.

It was at this point, Thordarson says, that he was forced to come clean to WikiLeaks. He says he told Assange about everything he had turned over to the FBI and forwarded to WikiLeaks all of his emails with the alleged FBI agents. Unsurprisingly, Assange "wasn't happy," he says. Hrafnsson, the WikiLeaks spokesman, told me he believed Thordarson was guilty of "pathological" behaviour, adding that the FBI's apparent recruitment of Thordarson had revealed the US government's "relentless persecution" of WikiLeaks. Thordarson, however, does not seem fazed by the controversy he has created. He now spends much of his time working for companies that offer security and bodyguard training in Iceland and Denmark, though does not believe his relationship with the FBI has "formally ended." He claims that his handlers at the bureau told him that he might yet be asked to testify in court about WikiLeaks. The Justice Department declined to comment about Thordarson but confirmed that its investigation into WikiLeaks is ongoing. Eventually, the US government may attempt to prosecute Assange, and there can be little doubt that he remains fixed firmly in the feds' crosshairs. The WikiLeaks founder's lawyers believe that a grand jury probe may already have produced an indictment against him that remains under seal – and so he remains sheltered in Ecuador's London Embassy, fearing that if he sets foot outside the door he will subsequently be extradited to the United States and thrown in jail.

But the prospect of this does not appear to be weighing heavily on Thordarson's mind. Only once, when recounting the time he spent passing information on Assange to the FBI, does his voice tremble with a quiver of guilt. "If you come into Julian's inner circle," Thordarson says, "he really takes care of his friends." Loading Ryan Gallagher is a London-based journalist who reports regularly on surveillance technology for Slate. Slate