U.S. authorities want to extradite Assange to face charges that he directed the publication of a huge trove of secret documents that disclosed the names of people who provided confidential information to American and coalition forces in Iraq and Afghanistan.
Assange, 47 and originally from Australia, is serving a 50-week sentence in London after being evicted from the Ecuadorian Embassy in April. He has insisted he will fight extradition.
Though the United States and the United Kingdom have a longstanding extradition treaty, one exception is for political offenses. The criteria aren't clearly spelled out, but Assange and his lawyers are likely to use the charges filed Thursday to argue that the Justice Department wants to put him on trial for crimes that are inherently political in that they involve the acquisition and publication of government secrets.
"At least on the face of it, it seems like it would complicate the ability of the United States to extradite Assange from the U.K. because we often think of espionage as one type of political offense," said Ashley Deeks, a University of Virginia law professor and national security and international law expert.
She said she regarded an initial indictment made public last month - charging Assange with a single count of conspiring with former Army intelligence analyst Chelsea Manning to hack a Defense Department computer password - as an attempt to "thread the needle and allege an underlying offense that did not seem like a political offense."
Whether the new Espionage Act charges fit the traditional definition of espionage, and by extension a political offense, may be murkier. "The question remains, how will the U.K. decision-makers think about this case," Deeks said.
That view was echoed by Stephen Vladeck, a national security law professor at the University of Texas at Austin.
"I don't think it's an especially meritorious argument that the new charges against Assange would fall within that exception, but it's certainly a more plausible argument than the original indictment," Vladeck said. "Now Assange's lawyers can argue with a straight face to a British court that some of what he's being prosecuted for is politically motivated."
Assange's lawyer, Barry Pollack, hinted at that argument after the new indictment was announced Thursday, saying "the fig leaf that this is merely about alleged computer hacking has been removed."
A senior Justice Department official, who discussed the prosecution with reporters Thursday on the condition of anonymity, wouldn't go into detail on how the new indictment might affect extradition, saying that Assange will have a "full and fair opportunity to raise all legal objections that he can, and a British judge will rule."
The extradition process was always going to be complicated in this case.
Swedish prosecutors have said they are reviving a rape investigation of Assange and will also seek his extradition. It's not clear which country would get Assange first. It will be up to a British court - as well as a senior Cabinet official with final say on extradition matters - to determine which claim takes priority.
One factor that may tip in favor of the U.S. is that British authorities tend to have less tolerance for disclosure of national security secrets, Vladeck said. On the other hand, he said, British authorities could also be wary of extraditing a defendant who faces the prospect of a long prison sentence.
Assange faced a maximum sentence in the first indictment of five years. Each of the 17 Espionage Act counts he faces in Thursday's indictment carries a maximum 10-year sentence.
No matter what happens, Vladeck added, "Extradition cases, even routine ones, are often so much more about the politics than the law."
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