A 29-year-old former CIA employee, Snowden has identified himself as the person who gave the Guardian and the Washington Post classified documents about how the US National Security Agency obtained data from US telecom and Internet companies.
While preparing his leaks, Snowden left Hawaii for Hong Kong on May 20 so he would be in a place that might be able to resist US prosecution attempts, he told the Guardian.
"Mainland China does have significant restrictions on free speech but the people of Hong Kong have a long tradition of protesting in the streets, making their views known," Snowden, a US citizen, said in a video interview posted on the Guardian's website.
"I believe that the Hong Kong government is actually independent in relation to a lot of other leading Western governments," he said from his hotel in the territory.
The NSA has requested a criminal probe into the leaks and on Sunday, the US Justice Department said it was in the initial stages of a criminal investigation.
Any prosecution of Snowden would likely come under the Espionage Act of 1917, the same law the US government has used against other civilians who have disclosed classified information without authorisation.
The United States and Hong Kong signed their extradition treaty in 1996, a year before the former British colony was returned to China. It allows for the exchange of criminal suspects in a formalized process that may also involve the Chinese government.
The treaty went into force in 1998 and provides that Hong Kong authorities can hold Snowden for 60 days, following a US request that includes probable cause, while Washington prepares a formal extradition request.
Some lawyers with expertise in extraditions said it would be a challenge for Snowden to circumvent the treaty if the US government decides to prosecute him.
"They're not going to put at risk their relationship with the US over Mr Snowden, and very few people have found that they have the clout to persuade another country to go out of their way for them," said Robert Anello, a New York lawyer who has handled extradition cases.
That is especially true when, as in this case, there is no third country to object. "If you're an American citizen, fleeing the US isn't such an easy thing," Anello said.
In March, a former equities research analyst, Trent Martin, was extradited to New York to face charges of insider trading. He had been arrested in Hong Kong in December and has pleaded not guilty.
Other suspects were extradited for smuggling charges, suspicion of violating controls on military exports, investment fraud charges and the alleged sale of illegal prescription drugs, according to US prosecutor statements at the time.
Douglas McNabb, a Houston lawyer who specializes in extradition, said he was surprised to hear that Snowden had chosen Hong Kong as a safe haven given the existing treaty.
"Probable cause won't be hard," McNabb said. "This guy came out and said, 'I did it.' His best defense would probably be that this is a political case instead of a criminal one." The treaty prohibits extradition for political cases.
Because Hong Kong is under the ultimate control of China, the treaty also allows for the refusal of transfers that would implicate the "defense, foreign affairs or essential public interest or policy" of China.
Another defense for Snowden, lawyers said, would be to argue a lack of "dual-criminality" - for a person to be extradited, the alleged act must be a crime in both countries.
While that will be for a Hong Kong court to decide, it might be a long shot, Anello said. "My guess is they will be able to find a law in Hong Kong that is very similar" to the U.S. Espionage Act, he said.
Hong Kong has not agreed to every US request for a prisoner transfer.
In 2008, Hong Kong released without explanation an Iranian operative whom Washington had accused of trying to obtain embargoed airplane parts. Yousef Boushvash was in custody with a criminal complaint on file in New York, so his release angered US officials.
It was not immediately clear whether Snowden had a lawyer.
Jesselyn Radack, a former Justice Department lawyer who represents whistleblowers, said she expected prosecutors would "try to indict him as soon as possible" with "voluminous" Espionage Act charges followed by Interpol warrants for his arrest.
But she said Snowden fit the profile and legal definition of a whistleblower and should be entitled to protections under a federal law passed to protect people who reveal waste and abuse.
"He said very clearly in statements that he's given that he was doing this to serve a public purpose," Radack said.
Asked if he had a plan in place, Snowden told the Guardian: "The only thing I can do is sit here and hope the Hong Kong government does not deport me ... My predisposition is to seek asylum in a country with shared values. The nation that most encompasses this is Iceland. They stood up for people over Internet freedom. I have no idea what my future is going to be."