The FBI has reportedly raided the home of a "second Snowden" suspected of leaking classified details of the US government's secret terrorist watch list.
Investigators have suspected since August that an unknown individual was following Edward Snowden's example and using their government position to leak US secrets.
Stories published by The Intercept, a news website run by Glenn Greenwald, an American journalist who worked with Snowden, caused a frantic government hunt for the second leaker.
The FBI has identified a suspect and searched their home in northern Virginia, just outside Washington DC, according to reports. The suspect is said to work for a private company hired by the federal government, the same role Snowden used to extract details of the National Security Agency's (NSA) mass surveillance programmes.
It is not clear what, if any, evidence the FBI recovered as no arrests are believed to have been made and the suspect has not been charged. The FBI declined to comment.
Rumours of a second leaker began to circulate after The Intercept published a classified document detailing who the US government includes on its database of suspected terrorists. The National Counterterrorism Centre (NTC) document appeared to show that almost half of the 680,000 people in the database had "no recognised terrorist group or affiliation".
The document raised questions about whether the US was taking an overly broad approach to listing terrorist suspects and led the NTC to report that a potential crime had been committed.
In Citizenfour, a new documentary about Snowden, Mr Greenwald appears to confirm that he had secured a second source inside the US government.
Mr Greenwald is shown meeting Snowden in Moscow, where the whistleblower has sought asylum from US criminal charges, and telling him of the new source. "The person is incredibly bold," Snowden said, after learning the details of the leaks. Mr Greenwald replied: "It was motivated by what you did."
Jeremy Scahill, the journalist behind the most recent story on The Intercept, said the leaker was "an extremely principled and brave whistleblower" but did not confirm their identity.
While Snowden fled to Hong Kong after stealing classified documents, the suspected second leaker appears to have stayed in the US and the FBI believes it is now closing in.
Snowden's leaks came after Chelsea Manning, formerly Bradley Manning, a US army soldier, handed over hundreds of thousands of secret documents to WikiLeaks and the US has long feared that Snowden would inspire "copycats".
"The degree that people have been lionising Snowden, it encourages people to make a name for themselves by leaking," Adam Schiff, a Democrat congressman on the House intelligence committee, told CNN.
Snowden was charged in June last year with espionage and theft of government property. If he returns to the US and is convicted he could face up to 30 years in prison. Manning was sentenced to 35 years in a military prison.
If the "second Snowden" is charged they could face a similar lengthy sentence. The White House has charged seven people with espionage since Barack Obama became president in 2009.
A friend of Dzhokhar Tsarnaev, the Boston marathon bombing suspect, was convicted yesterday of lying during the investigation into the 2013 attack, which killed three and injured more than 260.
Robel Phillipos, 21, was convicted of two counts for lying about being in Tsarnaev's dormitory while two other friends removed a backpack containing fireworks and other potential evidence. He faces up to 16 years in prison. He is due to be sentenced on Jan 29. Tsarnaev, who denies 30 federal charges, is awaiting trial.