Lowering his slight body to the floor, Souleymane Guengueng bent over and braced his legs close to his body, demonstrating how he was forced to spend seven months while restricted to a 6-foot-square prison cell with eight other prisoners.

“You ate there, you defecated there, that was my universe,” Mr. Guengueng, 54, said in French at the International Center of New York, located in Chelsea.

Fifteen years after almost dying of dengue as a prisoner in Chad, Mr. Guengueng said he is studying English to ensure the terrors inflicted during the 1980s by the country’s ruthless dictator will not be forgotten.

Yesterday, speaking over the quiet chatter of English learners, Mr. Guengueng, a dignified man with three tribal markings scratched down the side of his face, recalled the horrors he and his countrymen endured.

He was beaten and left to die. At one point, he was restricted to pitch-black darkness, unable to see a hand in front of him. In a cell next to his, female prisoners ripped out their own hair and hung themselves with it; guards burned off some women’s breasts.

Mr. Guengueng is just one of hundreds of thousands of victims of the eight-year rule of Hissene Habre in the destitute Central African nation.

This week, survivors and widows of the victims scored a long-awaited victory when Mr. Habre was arrested in Senegal, where he has been living in exile. The former dictator has been charged in Belgium with human rights atrocities. Senegal complied with that nation’s demands to apprehend him.

Mr. Guengueng played a large role in the action taken against Mr. Habre, but few were there to celebrate with him in New York. Nearly a year ago, he left behind his 10 children, five grandchildren, and his wife in Chad to undergo medical services at Bellevue Hospital’s program for survivors of torture and to work on the case.

Surviving in New York is not easy, admitted Mr. Guengueng, a man not inclined to complain about his own situation.

He has no Chadian friends in New York, and he rents a room from a family in Harlem for $450 a month. “Some days, I just eat very little to save money to send it back to my family,” he said.

The International Center of New York has been a haven. “It’s a privilege to learn here,” he said. “I meet people from all over the world.”

Mr. Guengueng, who already speaks six languages and dialects – from his native Kim to French and Arabic – is just one student among many struggling to master English at the center. His mission and drive, however, are unique.

“I have talked in so many places about the fight for justice,” he said, ticking off locales around Europe and throughout America. The ability to deliver his message in English, he said, would make it more effective.

His campaign to make sure the world does not forget what happened in Chad began in 1991, shortly after he was freed after two years in prison on charges of being part of the opposition. In his free time, Mr. Guengueng, an accountant, went door to door in Chad with other survivors, collecting victims’ and relatives’ memories of abuse.

Mr. Habre was installed in 1982 with American support to serve as a bulwark against Libya’s Muammar Gadhafi. Mr. Habre’s reign was marked by widespread terror. There were 40,000 political killings and 200,000 victims of torture, according to the Chadian Ministry of Justice’s 1992 Commission of Inquiry.

The evidence Mr. Guengueng collected was crucial in forming a case against Mr. Habre. “He is the public face of the suffering of thousands of victims,” the special counsel of Human Rights Watch, Reed Brody, wrote in an e-mail from Senegal. “He is the rock on which we have built the campaign. It was his force of personality that brought the victims together, it was his charisma that convinced the Belgian government that it had to allow the dossier to go forward.”

After this week’s arrest in Senegal, the next step, which will be challenging, is to ensure Mr. Habre’s extradition to Belgium. If that happens, Mr. Guengueng plans to be there – and to testify in English.