Last week, several Republican senators, including John McCain, called on President Obama to stop releasing detainees from the prison at Guantanamo Bay, Cuba. Their argument was that after the terror attacks in Paris, the 122 prisoners still in Guantanamo should be made to stay right where they are, where they can do the West no harm.

On Tuesday, one of those detainees, Mohamedou Ould Slahi, who was sent to Guantanamo in 2002 and remains there to this day, is poised to offer a powerful rejoinder. Three years into his detention . years during which he was isolated, tortured, beaten, sexually abused and humiliated . Slahi wrote a 466-page, 122,000-word account of what had happened to him up to that point.

His manuscript was immediately classified, and it took years of litigation and negotiation by Slahi’s pro bono lawyers to force the military to declassify a redacted version. Even with the redactions, “Guantanamo Diary” is an extraordinary document . “A vision of hell, beyond Orwell, beyond Kafka,” as John le Carre aptly describes it in a back cover blurb . that every American should read.

A native of Mauritania, Slahi, 44, is fluent in several languages . he learned English while in Guantanamo . and lived in Canada and Germany as well as the Muslim world. He came under suspicion because an Al Qaeda member, who had been based in Montreal . where Slahi had also lived . was arrested and charged with plotting to bomb the Los Angeles International Airport in 1999. Slahi was questioned about this plot several times, but he was always released. After 9/11, Slahi was detained again for questioning. That time, he was turned over to the American authorities, in whose captivity he has been ever since.

What was he accused of? Slahi asked this question of his captors often and was never given a straight answer. This, of course, is part of the problem with Guantanamo, a prison where being formally charged with a crime is a luxury, not a requirement. His efforts to tell the truth . that he had no involvement in any acts of terrorism . only angered his interrogators. “Looks like a dog, walks like a dog, smells like a dog, barks like a dog, must be a dog,” one interrogator used to say. That was the best his captors could do to explain why he was there. Yet the military was so sure he was a key Al Qaeda player that he was subjected to “special interrogation” techniques that had been signed off by the secretary of defense, Donald Rumsfeld, himself.

“Special interrogation techniques,” of course, is a euphemism for torture. The sections of the book that describe his torture make for harrowing reading. Slahi was so sleep-deprived that he eventually started to hallucinate. Chained to the ground, he was forced to “stand” in positions that were extremely painful. Interrogators went at him in shifts . 24 hours a day. Sometimes during interrogations, female interrogators rubbed their breasts over his body and fondled him.

It is hard to read about his torture without feeling a sense of shame.

Does Slahi crack? Of course: to get the torture to stop, he finally lied, telling his interrogators what he thought they wanted to hear, just as torture victims have done since the Inquisition. “Torture doesn’t guarantee that the detainee cooperates,” writes Slahi. “In order to stop torture, the detainee has to please his assailant, even with untruthful, and sometime misleading [intelligence].” McCain, who was tortured in Vietnam, knows this; last month, he made a powerful speech in which he condemned America’s use of torture, saying, “the use of torture compromises that which most distinguishes us from our enemies, our belief that all people, even captured enemies, possess basic human rights.” That is also why it is so disheartening that McCain has allied himself with those who want to keep Guantanamo open.

In 2010, a federal district judge ruled in favor of Slahi’s habeas corpus petition because the evidence against him was so thin. The government appealed, and the order remains in limbo.

I asked Nancy Hollander, one of Slahi’s lawyers, to describe her client. “He is funny, smart, compassionate and thoughtful,” she said. All of these qualities come through in his memoir, which is surprisingly without rancor. “I have only written what I experienced, what I saw, and what I learned firsthand,” he writes toward the end of his book. “I have tried not to exaggerate, nor to understate. I have tried to be as fair as possible, to the U.S. government, to my brothers, and to myself.” One of the wonders of the book is that he does come across as fair to all, even his torturers.

But the quote that sticks with me most is something that one of his guards told him, something that could stand as a fitting epitaph for Guantanamo itself: “I know I can go to hell for what I did to you.”