President Obama, left, and Attorney General Eric H. Holder Jr. (Pablo Martinez Monsivais / Associated Press)

Thanks to a single federal court filing, Fox News reporter James Rosen got tangled up in a federal leak investigation against State Department security analyst Stephen Jin-Woo Kim, who allegedly passed along classified information to Rosen for a June 11, 2009, FoxNews.com story on North Korea. The government has indicted Kim under the Espionage Act.

As it pursued evidence against Kim, the government got ahold of his personal e-mail account, where it found some revealing correspondence with Rosen. The two had decided to use aliases in the exchanges, and Rosen expressed his ambition to break news “ahead of my competitors” and to get his hands on “internal memos.”

Such exchanges, however, weren’t enough. The government also wanted to snoop on Rosen’s own personal Gmail account. It cited “probable cause” that such an investigative route would yield “evidence material to this investigation.” To make the case that it should have access to the reporter’s e-mail account, the Justice Department, in the search warrant affidavit, alleged that there was reason to believe that Rosen himself had been a co-conspirator in violating the Espionage Act. Along with other leak-investigation activity, that assertion ignited Washington, as critics of many political persuasions alleged that Attorney General Eric Holder was criminalizing journalism.

Just how badly did the government need those personal e-mails of James Rosen? How necessary was it to suggest that he was an “aider and abettor and/or co-conspirator” just to get access to such correspondence?

Some recently surfaced court documents help answer those critical questions. Last week, a federal D.C. court released a flurry of highly redacted filings that showcase a fight between Kim’s defense lawyers and government prosecutors over evidence in the case. In a towering set of motions, counsel for Kim had asked the government for all manner of information that might contextualize or excuse the alleged behavior of the State Department analyst. For instance, Kim wanted the goods on other intelligence leaks regarding North Korea.

The idea: Perhaps it was someone else, not Kim, who passed along the sensitive information to Rosen.

In opposing the request for troves of documents, prosecutors came forth with some information on the strength of their case. For instance, the government wrote, “Even assuming that the defendant could establish the identity of a third-party perpetrator for one or more other unauthorized disclosures, he could not show the requisite similarity to the charged crime here. None of the alleged unauthorized disclosures identified by the defendant concern [redacted].” Translation: Authorities appear to have drawn a pretty straight line between Kim’s activity and the North Korea scoop published by Rosen — which came out just a little while after the two had corresponded and perhaps rendezvoused.

More from the government: “Without conceding that the United States had any obligation to do so, the government has searched for documents or information concerning any formal criminal investigation of unauthorized disclosures of national defense information by any of the 168 individuals who may have accessed the intelligence at issue. Nothing was found.”

Clearly the U.S. government didn’t need access to James Rosen’s personal e-mail account to reach those powerful condemnations. Judge Colleen Kollar-Kotelly even cited the government’s internal leak probes in denying a defense motion for government documents, though she conceded that she may revisit her ruling.

As the case wears on, the range of evidence and investigative tools available to the government will emerge, bringing ever greater context to the decision to seek Rosen’s private e-mails. Earlier this month, Justice put forth new guidelines that probably would have prevented the Rosen search warrant.

Erik Wemple writes the Erik Wemple blog, where he reports and opines on media organizations of all sorts.