Glenn Greenwald, one of the journalists who has worked closely with exiled whistleblower Edward Snowden to reveal the National Security Agency's mass surveillance programs, says there may be a second leaker providing the NSA's secrets to the press.

Two German media reports co-authored by former WikiLeaks volunteer and current Tor Project employee Jacob Appelbaum are the cause of his suspicion.

The first report was published in December by Der Spiegel and describes a 50-page catalog of NSA surveillance tools. The second came last week from the German broadcasters Norddeutscher Rundfunk (NDR) and Westdeutscher Rundfunk (WDR), detailing NSA surveillance of people who use Tor and other online privacy services.

Both articles "notably fail to mention anything about the sourcing for the documents," Greenwald tells U.S. News.