London’s High Court is expected to rule on whether it accepts US assurances that Assange, 52, will be given a fair trial and will not face the death penalty, and therefore can safely extradite him to the US. The ruling could pave the way for Assange to be transferred across the Atlantic to face 18 charges – all except one under the Espionage Act – over Wikileaks’s release of thousands of confidential US military records and diplomatic cables.

These include secret US military reports about the Afghanistan and Iraq wars released in 2010. WikiLeaks also published a US military video showing what it described as the “indiscriminate slaying of over a dozen people”, including two Reuters news staff, by Apache helicopters in Iraq’s capital, Baghdad.

The US said the release of confidential documents had imperilled the lives of its agents. The upcoming hearing could take the US a step closer to prosecuting the biggest security breach in its military history, setting a precedent that may have ripple effects for global media freedom.

What assurances is the US expected to provide?

The British court has sought two sets of assurances from the US before it can decide whether the extradition is lawful under domestic and international law.

In 2021, it asked the Joe Biden administration to provide diplomatic assurances that Assange would not be held in a maximum security prison or subject to “Special Administrative Measures”, which allow the US government to restrict a prisoner’s contact with the outside world. Critics claim these measures can result in people being held in solitary confinement for extensive periods of time.

During the court’s last hearing in March, it gave the US three weeks to provide guarantees that Assange, who was born in Australia, would be entitled to seek a First Amendment right to free speech in a US trial and that there would be no prospect for new charges carrying the death penalty.

The US responded to both requests with written assurances, paving the way for the decisive extradition hearing to take place on May 20.

How reliable are US assurances?

Critics say US assurances are not reliable because they contain caveats. Julia Hall, Amnesty International’s expert on counterterrorism and criminal justice in Europe, said they were “inherently unreliable because the US government gives itself an out”.

In court documents made public in July 2021, the US made written assurances to the United Kingdom that Assange would not immediately be detained in a maximum security prison but reserved the right to do so based on his conduct. “The way the US government has treated Assange thus far indicates pretty strongly that they’d find something that he would do that allegedly requires them to put him in a maximum security prison,” Hall told Al Jazeera.

Similarly, the more recent set of assurances issued on April 16 stated Assange would have the ability to raise and rely upon the First Amendment during trial, but included the caveat that a decision on its applicability would be “exclusively within the purview of the US courts”.

“What this is saying is that whether or not he will be able to argue a freedom of expression defence will be left up to the court,” Hall said. “So again, this is a non-assurance.”

Assange’s wife, Stella, who is also a human rights lawyer, said the guarantees were “blatant weasel words”. “The diplomatic note does nothing to relieve our family’s extreme distress about his future, his grim expectation of spending the rest of his life in isolation in US prison for publishing award-winning journalism,” she said.

What could London’s High Court decide?

London’s High Court could rule that the assurances provided by the US are sufficient and agree to the request for extradition.

Alternatively, the UK court could deem the US assurances not satisfactory and grant Assange permission to launch an appeal against extradition.

In a written decision on March 26, British judges found Assange had a “real prospect of success” in fighting extradition on three of the grounds on which he was seeking to appeal. They said such an appeal may not go ahead in the UK, however, if the US government provided “satisfactory assurances” addressing them.

What could the court’s decision mean for Assange?

If the High Court in London refuses US assurances on Monday, his appeal on these three grounds identified by the High Court judges can go forward.

If the court accepts the US assurances, however, Assange can be extradited to the US. His only remaining option would then be to appeal against extradition at the European Court of Human Rights (ECHR). The Strasbourg-based court could decide to issue interim measures, or an injunction against sending Assange to the US, until it can decide whether the UK government is complying with its obligation under the European Convention on Human Rights by deciding to extradite Assange.

The ECHR’s interim measures would prevent immediate extradition, allowing Assange to remain in the UK until the European court reaches a decision. This process can take several years but the court has powers to expedite the proceedings if it believes a person is kept in harsh prison conditions. It is unclear whether UK authorities would continue to detain Assange at the Belmarsh maximum security prison for the duration of the dispute, or whether he would be bailed.

Should the ECHR decide against ordering interim measures, Assange would be extradited and face charges in the US.

What are the implications of the High Court ruling for press freedom?

Human rights observers and organisations say that if the court decides to extradite Assange, this would establish a dangerous precedent and have a chilling effect on freedom of speech for publishers and journalists around the world.

“It’s not just Julian Assange in the dock,” Hall said. “Silence Assange and others will be gagged.”

US authorities, however, say Assange is not being prosecuted for the publication of the leaked materials but for the criminal act of conspiring to unlawfully obtain them and hacking.

The case lays bare the tension between the US Espionage Act – which criminalises a wide range of activities that critics say may bear little resemblance to classic espionage and which does not take account of a defendant’s motives – and the First Amendment, which protects those who publish classified information without government authorisation.

In an expert testimony submitted to the UK court in 2020, Jameel Jaffer, executive director of the Knight First Amendment Institute at Columbia University, said the case crossed “a new legal frontier”.

“The government’s use of the Espionage Act against government insiders who supply classified information to the press poses a serious threat to the ability of the press to inform the public about matters relating to war and security,” Jaffer said.

“Against this background, I believe that the indictment of Mr Assange must be understood as a deliberate effort… to deter journalism that is vital to American democracy. The government’s successful prosecution of him would certainly have this effect.”