Image source, ICRCImage caption, Abu Zubaydah has been held at Guantanamo Bay without charge for over a decade
According to the US government, Abu Zubaydah was a terrorist recruiter responsible for the destruction of hundreds of lives.
The George W Bush administration claimed he was an elusive master of disguise who inspired extremism, plotted attacks, and attracted new members to al-Qaeda until he was captured by the CIA.
But his alleged crimes did not give anyone the right to torture him, and on Wednesday Mr Zubaydah's story will lie at the centre of a case in the highest US court that could have far-reaching consequences globally.
The Palestinian has claimed that he was waterboarded, beaten, deprived of sleep, isolated and kept in painful 'stress positions' during interrogations at a secret CIA "black site" in Poland before being transferred to detention at Guantanamo Bay, where he has been held without charge since 2006.
Mr Zubaydah has attempted to subpoena two CIA contractors for a Polish criminal investigation into the black site. The black sites were a network of facilities around the world used by the CIA to house and interrogate terror suspects in the years following the 2001 September 11 attacks.
The US federal government, however, has blocked the subpoenas, arguing that releasing the information would harm national security.
The case is the first involving a Guantanamo Bay detainee heard by the Supreme Court in more than a decade and has wide implications for determining the limits of the US government's right to secrecy.
Image source, ReutersImage caption, Camp Delta at Guantanamo Bay
After being captured in Pakistan in March 2002, Mr Zubaydah was taken to CIA-run black sites in several countries, including Thailand and Poland.
While in CIA custody, Mr Zubaydah was questioned under torture.
A US Senate report later found that Mr Zubaydah's interrogations included 83 instances of waterboarding, as well as sleep deprivation and 11 days confinement in a coffin-like box. While in CIA custody, Mr Zubaydah also lost his left eye.
The Supreme Court case stems from a Polish investigation into whether Polish officials were complicit in the CIA's black site programme.
At the request of Polish investigators, in 2017 Mr Zubaydah's legal team sought testimony from CIA contractors James Mitchell and Bruce Jessen. Both men were psychologists who played a key role in the agency's interrogation programme following the September 11 attacks.
A federal district court later voided the subpoenas because of the risk that government secrets would be revealed in court. The ruling was based on a legal doctrine called the "state secrets privilege", which allows the government to withhold information in courts if it claims that disclosure could endanger national security.
US lawyers cited this doctrine to deny requests by Mr Zubaydah's lawyers to question the CIA contractors and obtain related government documents for the Polish case.
A higher court in California sided with Mr Zubaydah, however, ruling that such blanket denials went too far.
The Supreme Court justices will review that decision and, perhaps, rule on how much discretion judges should give the US government when making national security judgments.
In early 2020, both CIA contractors involved in Mr Zubaydah's case testified in a military tribunal in Guantanamo Bay regarding their interrogation of suspected September 11 plotters.
Additionally, both Mr Mitchell and Mr Jessen were deposed after being sued by the American Civil Liberties Union on behalf of two former detainees and the family of another detainee who died after being chained – partially nude – in a cold cell. The lawsuit was settled out of court.
"There's a tonne of information out there in the world about what these two guys did," said Charles Church, a long-time member of Mr Zubaydah's legal team, but who is not representing him in the Supreme Court hearing. "There's very little chance – or virtually no chance – that our nation's security is going to be put at risk," Mr Church argued.
To date, the CIA has never acknowledged that it ran a black site in Poland. In 2015, the European Court on Human Rights, however, found that Mr Zubaydah was held there and that it is "inconceivable" he was not tortured while at the facility.
US officials initially alleged that Mr Zubaydah – whose given name is Zayn al-Abidin Muhammad Husayn – was a high-ranking member of al-Qaeda and served as a senior lieutenant to Osama Bin Laden.
The Senate torture report later found that the CIA had "significantly overstated" Mr Zubayah's role in the organisation but that he was a member.
A secret diary belonging to Mr Zubaydah was released in 2013, after it was obtained by Al Jazeera. A portrait of Mr Zubaydah emerged in the pages of his journal that was more complex than the one that US officials had painted.
Mr Zubaydah started keeping the diary in 1990, when he was a teenager. He wrote most often when he was feeling upset, or lost. After a friend was killed, in the autumn of 1991, he turned to the journal for solace: "I opened my bag which was covered with dust," he wrote. "I got this notebook out of it and I held the pen and started writing." He continued to record his thoughts for more than a decade, until he was captured.
Personal details are revealed throughout its pages: a fan of the Irish singer, Chris de Burgh, Mr Zubaydah enjoyed music and poetry. He studied computer science in India, and during that time he experienced bouts of homesickness. "My only friend is the cigarette," he wrote in June 1990. When he was feeling down, his older brother would cheer him up by singing Chis de Burg's song, Sailor, to him.
He has publicly denied being an al-Qaeda member. Still, shortly after the 9/11 attacks, he wrote in his diary that he and his friends celebrated the events.
"Happiness was not enough. As soon as the news came out on the radio, lambs were slaughtered, and juice and sweets were distributed for several days. News on the radio reflected American threats and preparation (for retaliation), close to a world war, while we were in a state of elation."