WASHINGTON — US intelligence and law enforcement investigators have concluded that they may never know the entirety of what the former National Security Agency contractor Edward J. Snowden extracted from classified government computers before leaving the United States, according to senior government officials.
Investigators remain in the dark about the extent of the data breach partly because the NSA facility in Hawaii where Snowden worked — unlike other NSA facilities — was not equipped with up-to-date software that allows the spy agency to monitor which corners of its vast computer landscape its employees are navigating at any given time.
Six months since the investigation began, officials said Snowden had further covered his tracks by logging into classified systems using the passwords of other security agency employees, as well as by hacking firewalls installed to limit access to certain parts of the system.
“They’ve spent hundreds and hundreds of man-hours trying to reconstruct everything he has gotten, and they still don’t know all of what he took,” a senior administration official said. “I know that seems crazy, but everything with this is crazy.”
That Snowden was so expertly able to exploit blind spots in the systems of America’s most secretive spy agency illustrates how far computer security still lagged years after President Obama ordered standards tightened after the WikiLeaks revelations of 2010.
Snowden’s disclosures set off a national debate about the expansion of the NSA’s powers to spy at home and abroad, and have left the Obama administration trying to mend relations with allies after his revelations about US eavesdropping on foreign leaders.
A presidential advisory committee that has been examining the security agency’s operations submitted its report to Obama on Friday. The White House said the report would not be made public until next month, when Obama announces which of the recommendations he has embraced and which he has rejected.
Snowden gave his cache of documents to a small group of journalists, and some from that group have shared documents with several news organizations — leading to a flurry of exposures about spying on friendly governments. In an interview with The New York Times in October, Snowden said he had given all of the documents he downloaded to journalists and kept no additional copies.
In recent days, a senior NSA official has told reporters that he believed Snowden still had access to documents not yet disclosed.
The official, Rick Ledgett, who is heading the security agency’s task force examining Snowden’s leak, said he would consider recommending amnesty for Snowden in exchange for those documents.
“It’s worth having a conversation about,” Ledgett told CBS News. “I would need assurances that the remainder of the data could be secured, and my bar for those assurances would be very high. It would be more than just an assertion on his part.”
Snowden is living and working in Russia under a one-year asylum. The Russian government has refused to extradite Snowden, who was indicted by the Justice Department in June on charges of espionage and stealing government property, to the United States.
Snowden has said he would return to the United States if he were offered amnesty, but it is unclear whether Obama — who would most likely have to make such a decision — would make such an offer, given the damage the administration has claimed Snowden’s leaks have done to national security.
Because the NSA is still uncertain about exactly what Snowden took, government officials sometimes first learn about specific documents from reporters preparing their articles for publication.
With the security agency trying to revamp its computer network in the aftermath of what could turn out to be the largest breach of classified information in US history, the Justice Department has continued its investigation of Snowden.
Some US officials said the security agency has been slow to install software that can detect unusual computer activity carried out by agency’s workers.