"The threshold for 'cruel, inhuman and degrading' is pretty high particularly when the country in question is the U.S. It has succeeded in relation to Russian prison conditions. It is arguable in the light of Bradley Manning but you would need to find a country which is willing to take on the U.S. and say that its treatment of prisoners breaches Article 3 of the European Convention on Human Rights," she said.
Bradley Manning, the U.S. soldier accused of providing classified information to website WikiLeaks, has claimed he has been mistreated in custody. In 2011, Manning's lawyer filed a formal complaint alleging his client had been stripped, denied his glasses and confined to a cell for 23 hours a day with no pillow, sheets or personal items.
Manning is appearing before a court-martial this week after pleading guilty to 10 of 22 charges against him and faces up to 20 years in jail.
Scenario 4: He makes a run for it...
Being spirited away on a plane or a boat might be attractive options for Snowden to escape Hong Kong authorities, if his visa is about to expire and the U.S. has yet to make its move.
Young said until the U.S. files an arrest warrant -- or even a provisional one -- there's no onus on carriers to report Snowden's presence if he turns up at a departure gate.
"It may well be that informally that there are channels 'that these are individuals, if you do come across them let us know please' but nothing that obligates them to do this," he added.
CNN asked a number of airlines whether they've been asked by authorities report Snowden. Cathay Pacific said in a statement: "For privacy and security reasons, it would be inappropriate for us to discuss communications, if any, received from governmental agencies. It would be up to the sending agency to share the information it deems appropriate." Qantas and Virgin Atlantic gave a similar response.
If Snowden was able to make it onto a vessel, U.S. authorities would be limited in their ability arrest him, even if they were on board, said Dr Zhao Yun, associate professor at the University of Hong Kong.
"That would be a violation of the sovereignty of the airline," Zhao said, adding that the country where the airline is registered has jurisdiction over the flight. The same applies for ships, except in the case of piracy.
However, he said if the alleged crime was serious enough -- for example, crimes against humanity, torture, slavery and hijacking -- universal jurisdiction kicks in.
"Crimes subject to universal jurisdiction are considered crimes against all (the entire world community)," he said, adding "In this sense, I do not think universal jurisdiction shall apply in (Snowden's) case."
Scenario 5: U.S. issues an arrest warrant and he's detained
This could be the worst case scenario for Snowden. If the U.S. issues a surrender warrant, Snowden could be detained by authorities in Hong Kong, after first being given the go-ahead by the territory's chief executive to arrest him.
Once detained, Young said Snowden would likely appear in an open court where a magistrate would decide whether there is enough evidence to commit him to trial.
Based on that decision, Hong Kong's chief executive would then decide whether to approve the surrender order and send Snowden back to the U.S.
Under Hong Kong law, the surrender order could be blocked if it appears that the offense is of a political nature or if the alleged offender might be punished on the basis of his or her political opinions.
However, other considerations would be the 1996 treaty between the U.N. and Hong Kong which takes precedence over the relevant law and includes a clause on "offenses involving the unlawful use of computers," Young said.