Guantánamo Diary. By Mohamedou Ould Slahi. Edited by Larry Siems. Little, Brown; 432 pages; $29. Canongate; £20. Buy from Amazon.com, Amazon.co.uk

MOHAMEDOU OULD SLAHI is the sort of person who attracts interest from Western spy agencies. A Mauritanian by birth, he joined al-Qaeda in 1991 when the group was fighting Afghanistan’s communist government. He left Afghanistan in 1992, claiming to have severed all ties with al-Qaeda, and lived in Germany and, briefly, Canada. In 2000, on his way back to Mauritania, he was arrested in Senegal. The Americans wondered if he had been part of the “Millennium plot”, a plan involving the bombing of Los Angeles airport—but could find no evidence.

The destruction of the World Trade Centre in New York, on September 11th 2001, and the launch of the “War on Terror” reignited the Americans’ interest. On November 20th 2001 Mr Slahi was asked by Mauritanian police to accompany them to the police station. No need to worry, they said—he wouldn’t be gone long. Instead, after eight days of interrogation, he was sent to Jordan, a country with a reputation for torturing its prisoners. Eight months later he was hooded, handcuffed and bundled aboard a military aeroplane, which flew him to America’s offshore prison camp at Guantánamo Bay in Cuba. He has been there ever since.

“Guantánamo Diary” was written in 2005, after the authorities granted Mr Slahi access to pen and paper in return for his co-operation. When he started it, the descriptions of torture, abuse and the American government’s contempt for the principles enshrined in the constitution were shocking. But its publication has been delayed by years of legal wrangling. Now, especially in the aftermath of the Senate’s report on torture, released in December, its contents are merely sickeningly familiar.

It is compelling reading nonetheless, chiefly for its contents but also because of the idiosyncratic command of English that Mr Slahi picked up mainly during his confinement. He vividly describes being deprived of sleep for days on end and chained to the floor of freezing cold rooms. He is force-fed seawater, sexually molested, subjected to a mock execution and repeatedly beaten, kicked and smashed across the face, all spiced with threats that his mother will be brought to Guantánamo and gang-raped. At one point, Mr Slahi admits to his interrogators that he is beginning to hear voices that aren’t there. But the torture, he says, failed—not to make him talk, but to tell the truth. Instead, he writes, he simply admitted to anything he thought his jailers might want to hear.

Their actions are baffling and often contradictory: an interrogator questions him about a suspected terrorist who travelled to Iraq in 2003—even though, as his captors knew full well, Mr Slahi had been in prison since 2001 and could not possibly know the answer. The book is also shot through with thick black “redaction” marks, in which an American censor has deemed certain passages too secret to be published. Yet information that is blacked out on one page is often freely available a few pages later; at other times it is trivially easy to deduce what the missing words must be from the surrounding context.

Fourteen years after his trip to the Mauritanian police station, Mr Slahi remains in Guantánamo Bay. Throughout the book, he protests his innocence, maintaining that he had cut his ties to radical Islamism in the early 1990s. It is impossible for his readers to know whether that is true. But a federal judge reviewed the government’s evidence against him, found it wanting, and in 2010 ordered Mr Slahi’s release. Barack Obama’s government appealed, and the case remains pending. Ten years after penning his diary, and with the world’s most powerful democracy having failed to give him a trial, Mr Slahi remains in jail.