More than six years after Mohamedou Ould Slahi finished writing, his editor finally got his hands on the text. This is the story of the battle for publication

In the summer and early autumn of 2005, Mohamedou Ould Slahi handwrote a 466-page, 122,000 word draft of his book in his single-cell segregation hut in Camp Echo, Guantánamo. He wrote it in instalments, starting not long after he was finally allowed to meet with Nancy Hollander and Sylvia Royce, two attorneys from his pro-bono legal team. Under the strict protocols of Guantánamo’s sweeping censorship regime, every page he wrote was considered classified from the moment of its creation, and each new section was surrendered to the US government for review.

On December 15, 2005, three months after he signed and dated the manuscript’s last page, Mohamedou interrupted his testimony during an Administrative Review Board hearing in Guantánamo to tell the presiding officers:

“I just want to mention here that I wrote a book recently while in jail here about my whole story, OK? I sent it for release to the District [of] Columbia, and when it is released I advise you guys to read it. A little advertisement. It is a very interesting book, I think.”

But Mohamedou’s manuscript was not released. It was stamped “SECRET”, a classification level for information that could cause serious damage to national security if it becomes public, and “NOFORN”, meaning it can’t be shared with any foreign nationals or intelligence services. It was deposited in a secure facility near Washington DC, accessible only to those with a full security clearance and an official “need to know.”

For more than six years, Mohamedou’s attorneys carried out negotiations to have the manuscript cleared for release

For more than six years, Mohamedou’s attorneys carried out litigation and negotiations to have the manuscript cleared for public release. Mohamedou’s manuscript was finally cleared for public release, and a member of his legal team was able to hand it to me on a disk labelled “Slahi Manuscript – Unclassified Version,” in the summer of 2012. By then, Mohamedou had been in Guantánamo for a decade. A federal judge had granted his habeas corpus petition two years before and ordered him released, but the US government had appealed, and the appeals court sent his petition back down to the federal district court for rehearing. That case is still pending.

Mohamedou remains to this day in the same segregation cell where he wrote his Guantánamo Diary. I have, I believe, read everything that has been made public about his case, and I do not understand why.

Facebook Twitter Pinterest ‘I believe there will be a homecoming’ ... Larry Siems.

In the five years I have spent reading the record about Mohamedou Ould Slahi’s case, I have not been persuaded by my government’s vague and shifting explanations for why he is in Guantánamo, or by the assertions of those who defend his now 13-year detention by saying he is almost certainly, or possibly, a this or a that. My own sense of fairness tells me the question of what this or that may be, and of why he must remain in US custody, should long ago have been answered. It would have been, I believe, if his Guantánamo Diary had not been kept secret for so long.

When Mohamedou wrote the manuscript for this book nine years ago, in the same isolated hut where some of its most nightmarish scenes had very recently happened, he set himself a task. “I have only written what I experienced, what I saw, and what I learned first-hand,” he explains near the end. “I have tried not to exaggerate, nor to understate. I have tried to be as fair as possible to the US government, to my brothers, and to myself.”

He has, from everything I have seen, done just that. The story he tells is well corroborated by the declassified record; he proves again and again to be a reliable narrator. He certainly does not exaggerate: the record contains torments and humiliations not included in the book, and he renders several of those he does include with considerable discretion. Even when the events he recounts are at their most extreme, his narration is tempered and direct. The horrors of those events speak for themselves.

• Mohamedou Ould Slahi: “smart, witty, garrulous, and curiously undamaged”

This is the secret world of Guantánamo – a world of startlingly premeditated brutalities and of incidental degradations, but also a world of ameliorating gestures and kindnesses, of acknowledgements and recognitions, of mutual curiosities and risky forays across deep divides. That Mohamedou managed to experience all of this despite four years of the most arbitrary treatment imaginable and in the midst of one of Guantánamo’s most horrendous interrogations says a great deal about his own character and his humanity. It says even more about his skills as a writer that he was able, so soon after the most traumatic of those experiences, to create from them a narrative that manages to be both damning and redeeming.

Thirteen years ago Mohamedou left his home in Nouakchott, Mauritania and drove to the headquarters of his national police for questioning. He has not returned. For our collective sense of story and of justice, we must have a clearer understanding of why this has not happened yet, what will happen next.

Guantánamo lives on unanswered questions. But now that we have the Guantánamo Diary, how can we not at least resolve the questions in Mohamedou’s case?

When we do, I believe there will be a homecoming. When that happens, the redactions will be filled in, the Guantánamo Diary will be re-edited and amended and updated as he himself would have it, and we will all be free to see the Guantánamo Diary for what it ultimately is: an account of one man’s odyssey through an increasingly borderless and anxious world, a world where the forces shaping lives are ever more distant and clandestine, where destinies are determined by powers with seemingly infinite reach, a world that threatens to dehumanise but fails to dehumanise – in short, an epic for our times.

Larry Siems is a writer and human rights advocate, and for many years directed the Freedom to Write Program at PEN American Center.

• Listen to live and recorded readings by Brian Eno, Colin Firth and others, as well as a panel discussion with Slahi’s lawyer and brother about this remarkable account of imprisonment. Guardian Live: Guantánamo Diary, Tuesday 20 January, 7pm, London

• Guantanamo Diary is published on Tuesday 20 January. To buy a copy for £15 (RRP £20), visit bookshop.theguardian.com or call the Guardian Bookshop on 0330 333 6846. Free UK p&p on online orders over £10. A £1.99 charge applies to telephone orders