Top experts say there could be a new person leaking details about the National Security Agency, in addition to former contractor Edward Snowden.

Glenn Greenwald, the journalist most closely associated to Snowden, said he suspects someone else has been involved in leaking out new documents, and other experts have backed up the claim.

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The existence of a second leaker “seems clear at this point,” Greenwald wrote on Twitter over the weekend.

“The lack of sourcing to Snowden on this & that last [Der Spiegel] article seems petty telling,” he added, after German broadcasters reported that the NSA was tracking people searching for details about privacy software.

Neither the Der Spiegel article from December nor last week’s story, both of which were partly written by privacy advocate and security researcher Jacob Appelbaum, specifically mentioned that the information emanated from leaks by Snowden.

“That's particularly notable given that virtually every other article using Snowden documents - including der Spiegel - specifically identified him as the source,” Greenwald said in an email to The Hill on Monday.

Other people who have seen Snowden’s trove of documents have agreed that the documents revealed by German outlets seem to indicate a second source.

Bruce Schneier, a cryptologist and cybersecurity expert who has helped the Guardian review Snowden’s disclosures, said he did “not believe that this came from the Snowden documents.”

“I think there’s a second leaker out there,” he wrote in a blog post last week.

If true, it could add another headache for the NSA, which has struggled for more than a year to contain the fallout from Snowden’s revelations. Defenders of the NSA say that the disclosures have hurt U.S. security and empowered terrorists and other enemies abroad.

Among other internal reforms, the spy agency has beefed up its clearance procedures to prevent another employee from passing along secret documents to journalists or governments in Beijing and Moscow.

“If in fact this is a post-Snowden NSA leak, then it’s probably just proof that you can always build a bigger mousetrap; that doesn’t mean you’re going to catch the mice,” said Stephen Vladeck, a law professor at American University who specializes in national security issues.

Vladeck added that leaks about controversial national security programs are in many ways inevitable, and may not be tied to Snowden’s leaks in any way.

For Greenwald, however, a second leaker would be affirmation of Snowden’s actions.

“I've long thought one of the most significant and enduring consequences of Snowden's successful whistleblowing will be that he will inspire other leakers to come forward,” he told The Hill.