WASHINGTON (AFP) - United States (US) authorities are looking into how a low-level information technology (IT) contractor managed to get hold of top secret documents that are usually accessible to only a small number of insiders, experts say.
Mr Edward Snowden's bombshell leaks about National Security Agency (NSA) spying included an order from the Foreign Intelligence Surveillance Court (Fisa), which has kept its documents secret for more than three decades.
"It's extraordinarily closely held," said Mr Robert Deitz, who served as general counsel for the NSA and the Central Intelligence Agency (CIA).
Fewer than 100 people likely would have permission to see such an order, Mr Deitz, a professor of public policy at George Mason University, told Agence France-Presse.
"Why is he gaining access to the crown jewels?" he said ofMr Snowden, who has no university degree or extensive intelligence training.
The wide range of information Mr Snowden exposed, which covered separate programmes, raised the possibility he may have exceeded his authorised access to get his hands on the secret files, former officials said.
"I think it's highly likely that he overstepped his bounds," said Mr Cedric Leighton, a former deputy director of training at the NSA and retired Air Force colonel.
"And all it took was him helping some senior person with an IT issue, and he may have had access to possibly that person's password. Once that happens, then all bets are off," said Mr Leighton.
Mr Snowden's leaks to The Guardian and Washington Post newspapers appeared to differ from the case of Bradley Manning, the American soldier now on trial for espionage after leaking a massive trove of secret files.
Manning, an army private working as an intelligence analyst in Iraq, appeared to have permission to trawl through a huge stream of classified diplomatic cables and military intelligence reports, which he later passed to the WikiLeaks website.
Mr Snowden was not an intelligence analyst and "he was supposed to be maintaining the network, but he was possibly looking at the traffic," said Mr James Lewis, a former US official specialising in cyber security.
The Manning case prompted calls to bolster security controls and limit the distribution of sensitive intelligence, after a decade in which the spy services worked to push information to the battlefront.
In the aftermath of the September 11, 2001, attacks, lawmakers slammed the spy agencies for hoarding crucial information and failing to "connect the dots" that could have averted the suicide airliner massacre.
The intelligence community faces a delicate balance between restricting information based on the "need to know" and the "need to share," but the Snowden case may cause the agencies to reconsider how secrets are managed, Mr Deitz said.
The latest leak inevitably will bring a thorough review of internal cyber security at the spy agencies and of how employees, particularly contractors, are vetted and screened, Leighton said.
"They will have to look at authentication systems. They will have to look at instituting something beyond what they've got now to really provide extra safeguards to all kinds of data," he said.
For the NSA, Mr Snowden was unusual for his lack of formal education and training, said Mr Leighton, as the NSA tends to recruit highly-qualified technicians and select only the highest scores for those applying from the military.
In media interviews, Mr Snowden also may have overstated how much secret information came across his screen or others at his level.
Any NSA analyst "at any time can target anyone, any selector, anywhere", Mr Snowden told The Guardian. "I, sitting at my desk, certainly had the authorities to wiretap anyone from you or your accountant to a federal judge to even the president if I had a personal email." But Mr Deitz dismissed the claim as "ridiculous." "It's complete crapola," he said.
Mr Snowden's claims not only ignore the procedures and legal approvals that would be required for any kind of wiretapping, but also seem to be reflect an Hollywood-type fantasy about how intelligence agencies work, he said.
"And no contractor at this level, or at any other level, is going to be able to do that."