In an effort to unmask a leaker who fed a reporter classified information about North Korea, FBI investigators tracked the journalist's movements in and out of a government building, obtained copies of e-mails from his personal account and also took the unprecedented step of alleging that the reporter engaged in a criminal conspiracy simply for doing his job.

Investigators tracked the reporter's movement using security badge access records as he left and returned to the State Department's headquarters in Washington, DC, and also obtained two days’ worth of e-mail correspondence from his Gmail account.

The FBI took the aggressive steps in 2009 against Fox News reporter James Rosen, the news outlet's chief Washington, DC correspondent, over a story Rosen published online in June that year, according to the Washington Post.

"Never in the history of the Espionage Act has the government accused a reporter of violating the law for urging a source to disclose information," Ben Wizner, director of the ACLU's Speech, Privacy and Technology Project said in a statement. "This is a dangerous precedent that threatens to criminalize routine investigative journalism."

The revelations come in an affidavit filed in an investigation against a State Department security adviser who is accused of leaking classified information to Rosen.

Although investigators had already zeroed in on Stephen Jin-Woo Kim, an employee of Lawrence Livermore National Lab and a security adviser to the State Department, as the suspect, and had examined Kim's computer and e-mails, federal investigators took the unprecedented step of telling a judge that Rosen was also a suspect in a criminal conspiracy to obtain classified information through Kim in order to obtain access to his Gmail account.

According to the affidavit (.pdf), FBI Agent Reginald Reyes told the judge there was probable cause to believe that Rosen had violated the Espionage Act by serving “as an aider, abettor and/or co-conspirator” in the leak. The federal judge found there was probable cause to believe that Rosen was a co-conspirator and approved the warrant.

It's the first time the Obama administration has accused a U.S. journalist of breaking the law in relation to a leak investigation. The Espionage Act is the same law that former Army intelligence analyst Bradley Manning is accused of violating when he leaked information to the secret-spilling site WikiLeaks.

The revelations about the Rosen investigation come in the wake of earlier news reports that federal investigators obtained the phone records of journalists for the Associated Press for a leak investigation into a different story published last year about a CIA operation in Yemen that halted an al-Qaida plot to detonate a bomb on an airplane headed to the U.S.

The new revelation adds to growing concerns that the Obama administration is bent on an aggressive campaign that not only is likely to stifle whistleblowers but also will stifle the press and its ability to properly perform the oversight role established by the Constitution.

In the AP investigation, the feds seized records for 20 separate phone lines, including the work and personal phone numbers of individual reporters, the general phone lines for AP bureaus in New York, Washington and Hartford, Connecticut, and a main number used by AP reporters in the House of Representatives. They did so with the approval of the Justice Department, which has insisted it followed its internal rules in signing off on the subpoena used to obtain the records.

In the AP case, the feds used an administrative subpoena to obtain the phone records, instead of a probable cause warrant, as they did in the Fox News case, which requires a judge's approval.

The investigation of Rosen began shortly after his story published in June 2009. In the article, Rosen reported that U.S. intelligence officials had obtained information that North Korea was likely planning to respond to United Nations sanctions over its nuclear activities with more nuclear tests. The information had come from a classified report distributed to the intelligence community the morning Rosen published his story.

According to the FBI affidavit, the report was distributed electronically to a small group within the intelligence community through a classified database. At least 95 people accessed the report, including Kim. But investigators found evidence that only one of those people, Kim, also had contact with Rosen on that day, though at least four others had contact with the reporter at other times.

Reyes told the judge that there was reason to believe that Kim had handed off the report to Rosen the day Rosen's story broke. According to forensic evidence of his computer, Kim accessed the report online several times the morning it was distributed. About fifteen minutes after he accessed it last at 11:48am, Kim allegedly left the State Department building to meet with Rosen to discuss the report. Phone records also show that he and Rosen had several brief phone conversations prior to the report being released and during the time that Kim had the report open on his computer.

Rosen worked out of a press booth at the State Department and, like government employees, used a security badge to enter the building. When investigators examined access records for Kim's and Rosen's security badges on the day the story published, they discovered that the two left and entered the State Department building within minutes of each other, suggesting they had gone outside for a private meeting to discuss the classified report.

"Mr. Kim departed DoS at or around 12:02 p.m. followed shortly thereafter by The Reporter at or around 12:03 p.m.; and Mr. Kim returned to DoS at or around 12:26 p.m. followed shortly thereafter by The Reporter at or around 12:30 p.m.," Reyes wrote in the affidavit.

A few hours later, Rosen published his story.

Kim and Rosen apparently used a covert system designed to conceal their identities. In their email exchanges, the two allegedly used aliases – Rosen referred to himself as "Alex" and to Kim as “Leo." Reyes notes that Rosen apparently assumed the alias of Alexander Butterfield, the person who was responsible for President Richard Nixon's secret recording system during his years in the White House.

Rosen and Kim also took other precautions. In one email exchange, Rosen instructed Kim that whenever other individuals wanted to speak with him, they would send a coded message to his Gmail account. “One asterisk means to contact them, or that previously suggested plans for communication are to proceed as agreed; two asterisks means the opposite.”

Despite these attempts at operation-security, Reyes noted that Kim accessed the Yahoo email account he used to communicate with Rose while logged in to his State Department computer, which was part of his undoing. Although Kim had deleted his email exchanges with Rosen, he apparently was unaware that simply moving a document to the trash wouldn't actually erase it from the computer. Forensic investigators found copies of the emails in the unallocated space of Kim's computer.

To support his claim that Rosen was involved in a criminal conspiracy, Reyes quoted an email exchange between Kim and Rosen, in which Rosen told him that he was interested in "breaking news ahead of my competitors” and had a particular interest in “what intelligence is picking up.” He also told Kim, “I’d love to see some internal State Department analyses.”

The suggestion is that Rosen broke the law by soliciting information from Kim, something that all journalists do routinely with sources.

Although the Justice Department generally follows stricter rules that limit when it will seek a reporter's phone records and correspondence, these protections disappear if a journalist is suspected of breaking the law. But it remains to be seen whether a reporter communicating with sources can be prosecuted for seeking information. It's a question that is at the heart of the government's investigation against WikiLeaks for publishing documents supplied by Manning. Manning is set to go to trial this summer for his role in leaking thousands of military and State Department documents to WikiLeaks. A grand jury investigation has also been investigating WikiLeaks for possible prosecution.