How Tahar Rahim transcended the prisons of ‘The Mauritanian’

For Tahar Rahim, “The Mauritanian” was about prisons — at Guantánamo Bay, and of the mind.

“It’s about the horrors he has been through, but also there’s a light inside of this character,” French-born Rahim says of playing longtime detainee and now bestselling author Mohamedou Ould Slahi. “The way he was able to go through this ... he became so wise to be able to not hold a grudge against anybody after all of this. It’s almost incredible for a human being.”

Slahi (also spelled “Salahi”) was accused by American intelligence of being a “significant Al Qaeda operative” involved in not only the 1999 millennium plot, but the 9/11 terrorist attacks. After initially claiming innocence, Slahi “confessed” under torture and was held without charge for 14 years. The film depicts his confinement and the legal battle waged by civil libertarians (played by Jodie Foster and Shailene Woodley) on his behalf. Slahi wrote the memoir on which “Mauritanian” is based, “Guantánamo Diary,” while in captivity. Rahim and Foster have received Golden Globe nominations for their performances.

Rahim met with Slahi and came away impressed: “That he came out as he is right now, a wise man and a good person .... He had faith in the fact that he is innocent, and he’s been fighting to tell people that.

“That’s why he’s saying at the very end [of the film, while still incarcerated but finally before a court], ‘Your honor, even here I can be free because now everybody could hear me.’ ”

When Slahi joined Al Qaeda’s jihad against Russian invaders in Afghanistan, he was fighting on the side backed by the CIA. According to him, he walked away from the organization in the early 1990s. However, his cousin became a top advisor to Osama bin Laden. Slahi’s rare contacts with the cousin, and an occasion in which he allowed travelers from near his hometown to stay the night — only to learn they were Al Qaeda soldiers — were among the circumstantial facts that convinced American intelligence he was an active Al Qaeda recruiter. Investigators never, however, found sufficient evidence to file charges.

“It’s 16 years, I think, from when he was arrested. If there was some proof, we would have found it,” Rahim says. “Then I talk with Nancy Hollander [Slahi’s lawyer, played by Foster] and some [intelligence] people that I know from ‘The Looming Tower’ [the Hulu series Rahim was in about the lead-up to 9/11]: ‘If that guy was guilty, don’t you think that the CIA, the FBI, the intelligence people, would have found something?’ And they said, ‘Yeah, they would have.’ ”

“The Mauritanian” isn’t actually about whether Slahi helped recruit or fund terrorists. It’s about the human spirit surviving brutality and incarceration, and also about the rule of law: specifically, the writ of habeas corpus, prohibiting unlawful and indefinite detention.

“We’re living in democracies, and there is the law, you know, except at Guantánamo Bay,” Rahim says of the infamous military detention center. “It’s so crazy that those type of things are happening in our free countries. Everybody has the right to have a lawyer, to be judged; this is our main foundation. It has to be respected.”

During the period covered by the film, Slahi was in a rough state, physically.

“I went on a drastic diet because he said, ‘I was as thin as a stick.’ I lost [around 25 pounds] within 20 days. I was muscular in a TV show, and I had to go to this project. I ate so much boiled eggs that I almost turned into a chicken, man. At some point that state leads you to an emotional place you wouldn’t know could exist.”

A devout Muslim, Slahi admitted to Rahim that he struggled with profound anger at his predicament but that it had no outlet because it was directed at God and not people.

“The only way to let it out is it has to evolve into something stronger, bigger, that could help you, finally. And this is wisdom,” Rahim says of his character’s journey. “Transforming that anger into strength. Yeah, I think that helped me the most.”

Of a scene in which, under extreme physical duress, Slahi hallucinates that his mother has been detained and tortured, Rahim says he couldn’t imagine the physical torture that brought Slahi to that point, but “we shared something very intimate, Mohamedou and I: the love of our mothers.

“I started to sob. My heart was broken, because I could see my mom here — I got goose bumps [right now, remembering it] — and I could shoot it just one time. Then I fell down, and I said, ‘I’m dead. I just can’t keep going. I hope you have it.’

“At this moment, I think I touched with the tip of my finger a little bit of what he’s been through. It was so heavy.”