Obama administration officials told the New York Times Saturday investigators have spent "hundreds and hundreds of man hours" piecing together Snowden's digital footprints in the months prior to his massive leak of classified documents to a group of reporters. But because tracking software ordered installed on all government computers hadn't been put in place at the Hawaii office where Snowden worked, much of his document gathering can't be traced.
In the months since Snowden fled the country and turned over the documents to reporters at the Times and elsewhere, reporters have been the government's prime source for information about what exactly Snowden took. The State Department has on numerous occasions only found out about a new Snowden leak when reporters sought comment prior to publishing a story about the latest revelations. the Times said.
"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," said a senior administration official whom the Times did not identify by name. "I know that seems crazy, but everything with this is crazy."
Officials said Snowden was very familiar with the NSA's computer hierarchy and the overhaul that President Barack Obama ordered in the wake of the 2010 WikiLeaks ordeal, during which Army Pfc. Chelsea Manning, formerly known as Bradley, a military intelligence analyst, stole a huge trove of classified military and diplomatic documents and turned them over to the anti-secrecy group for publication. Snowden, the Times said, was aware his Hawaii facility had not seen the tracking software installed, which allowed him to cull his trove of documents without arousing suspicion.
Rick Ledgett, the NSA official tasked with carrying out the Snowden investigation, said it's highly likely there are more documents out there than have been reported -- and said he would advise offering Snowden amnesty from prosecution in exchange for their return.
"So, my personal view is, yes, it's worth having a conversation about [offering amnesty]," 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 where he's been granted one-year asylum. Thus far, the Russian government has refused to extradite Snowden back to the United States, where he faces charges of espionage and stealing government property.