As surveillance whistleblower Edward Snowden hopscotches across the globe to avoid extradition to the United States, some wonder how mighty America could ever fail to catch its most famous fugitive.

But experts suggest that the intense public interest in the former National Security Agency contractor is helping him stay free, at least for now.

"This is a case where there are mixed feelings, so the United States is walking a tightrope, I think, with a lot of its own people who are really upset by what they've just found out," said Albert Berry, a professor emeritus in international economics at University of Toronto's Munk School for International Studies.

"The United States government probably doesn't want to appear very aggressive in this case, because their back is weak, so to speak."

Snowden, 30, has spent the last month in Hong Kong after leaking details about a secretive U.S. surveillance system called Prism that sifts through huge troves of phone and online data.

On Sunday, the U.S. fugitive wanted on espionage charges flew to Moscow, in what was described as the first leg in a journey to Ecuador.

But when Snowden failed to get on a connecting flight to Cuba as expected, U.S. authorities and media outlets around the world began wondering where the American was and what his plans actually were.

On Tuesday, Russian President Vladimir Putin revealed that Snowden was still in Moscow airport's transit zone. He said the country doesn't have an extradition treaty and won't be acquiescing to a U.S. request to hand the fugitive over.

The U.S. has amplified pressure on the already tense relationship between the countries. Russia said on Tuesday it would not accept any blame over Snowden's efforts to evade prosecution in the U.S.

"We consider the attempts to accuse the Russian side of violating U.S. laws, and practically of involvement in a plot, to be absolutely groundless and unacceptable," said Foreign Minister Sergei Lavrov.

Meanwhile, China on Tuesday denied it helped Snowden get out of its province of Hong Kong.

"The United States' criticism of China's central government is baseless. China absolutely cannot accept it," said Foreign Ministry spokeswoman Hua Chunying.

Espionage charges pose a problem

So far, though, American pressure has reaped little in the Snowden case.

Reports suggest the U.S. government has spent nearly 10 days seeking action by Hong Kong, a special administrative region of China, on the Snowden case, asking it early on to provisionally arrest him in anticipation of his extradition. The U.S. also revoked his passport.

But on Sunday, Snowden flew safely to Moscow. Asked for an explanation, Hong Kong officials blamed the process for his escape, saying the U.S. failed to "comply with legal requirements under Hong Kong law."

Snowden left Hong Kong on Wednesday in search of a new haven. (The Guardian/Associated Press)

White House spokesman Jay Carney said he didn't "buy" the technical issue, but by that point U.S. officials were focused on pressuring Russia to hand over Snowden.

Media reports suggest the U.S. could have requested an Interpol red notice, essentially an international arrest warrant sent out to all member countries, but espionage charges are considered political, a domain that Interpol avoids.

Snowden is charged under the 1917 Espionage Act with unauthorized communication of national defence information and wilful communication of classified intelligence, but he also faces the non-political charge of theft of government property.

Political charges help Snowden

The political nature of the key charges could also help Snowden skirt extradition treaty agreements.

Ecuador, Snowden's apparent destination, has an extradition treaty with the U.S., but it includes an exception for crimes or action of a political nature.

Vancouver-based extradition lawyer Gary Botting suggested that the official agreements between countries to transfer suspected or convicted criminals are often subject to the political climate.

"Extradition is always ultimately a political decision," said Botting.

On the other hand, the lawyer noted that even if Snowden lands in a country where there is no extradition treaty, that nation could negotiate a diplomatic solution for the single case.

But the public outrage and the politicization of the case currently works in Snowden's favour, ensuring countries are far more hesitant to acquiesce to the U.S. demands.

"The more it is politicized, the more likely it is that the country where he ends up will say, 'Well, we can't extradite him, because you're trying to extradite him for a political purpose or for a political reason or for a political crime,'" added Botting.

An online petition calling for the U.S. to fully pardon Snowden had by early Monday surpassed the threshold of 100,000 signatures necessary to secure an official response.

Botting said that the U.S. needs an overhaul of its strategy if it expects to succeed with extradition.

"If the United States wants him back, they're going to have to minimize the political part of it and stick to the legalities of it and be very persuasive of the minister of justice wherever he ends up," said Botting.

Nothing to lose for Ecuador

Ecuador, meanwhile, said Monday that it had received a request for asylum from Snowden, but had not yet decided what to do.

University of Toronto professor Berry said Ecuador is a small country, but one determined lately to defy the U.S., sometimes for domestic political gain.

"They don't feel they have a great deal to lose," said Berry, since Ecuador is not economically linked to the U.S.

Ecuador President Rafael Correa's left-wing government has railed against American imperialism and given the boot to a U.S. airbase in the country.

As well, Berry notes that any country willing to help Snowden will be regarded well by the general public. "They're kind of tapping into a lot of support around the world," he said.

WikiLeaks founder Julian Assange has spent the last year holed up in London in the safety of the Ecuadorian Embassy, where he was granted diplomatic asylum.

Watch your back

Amnesty International said Monday that no matter where Snowden lands, he has a right to seek asylum due to a "well-founded fear of persecution" he'd face in the U.S.

Even if the asylum bid fails, Widney Brown, senior director of international law and policy at Amnesty International, said "no country can return a person to another country where there is a substantial risk of ill-treatment."

Last year, the UN special rapporteur on torture said the American government used cruel and inhumane treatment toward Bradley Manning, the U.S. soldier arrested for allegedly passing classified material onto WikiLeaks, for holding him in solitary confinement for nearly a year.

Then again, some say trouble could find Snowden wherever he goes.

"It's not a James Bond world out there," said Botting, but he suggests that the deeper Snowden gets into the spy vs. spy world, the more care he'll need to take.

"You have to watch your back."