The Chadian Truth Commission estimates that Hissene Habre's regime may have killed up to 40,000 Chadians and practiced widespread torture during his rule from 1982 to 1990.
An official with the New York-based Human Rights Watch, Reed Brody, told reporters in Nairobi Monday he has personally seen the files of Habre's political police.
They describe in detail the abuse of more than 12,000 people, including some 1,200 who died in detention in the capital alone.
Clement Abaifouta is an administrator with the Chadian Association of Victims of Political Repression and Crime.
He was arrested in 1985 shortly after receiving a scholarship to study in Germany, and spent four years in jail being forced to bury his fellow prisoners who died.
"They used to put up to 100 person[s] in a small room," he said. "In Chad, between March and April you have 50 degrees [Celsius], so imagine that in the small room they put up to 100 persons. They used to die, to die, to die, in one day, maybe 10 can die. I remember that, one day, we buried up to 37 persons."
Mr. Abaifouta says he was given no reason for his arrest and detention, but suspects he was targeted because his uncle was a member of an opposition political party.
The former Chadian leader has been living in the West African country of Senegal since he was ousted in 1990.
In February 2000 a Senegalese court charged Habre with torture and crimes against humanity, and placed him under house arrest. But the following year, Senegal's highest court ruled that Habre could not be tried in Senegal for crimes committed elsewhere.
Following a four-year investigation by a Belgian judge, Belgium issued a warrant for Habre's arrest last September. Two months later, a Senegalese court said it could not rule on the extradition request, and a government minister said the African Union must decide where Habre's case should be heard.
Human Rights Watch's Reed Brody says the African Union's endorsement to bring Habre to trial in Belgium or an African country will send a powerful message to the rest of Africa.
"While the heads of state have the case of Hissene Habre before them, this is really a test case for impunity on the continent," said Mr. Brody. "Bringing Hissene Habre to justice should be a first step for Africa to try to break this cycle in which leaders brutalize their people, pillage their treasury, and then just join up with their bank accounts somewhere else."
Brody joins more than 30 civil society groups all over Africa that Monday issued a letter to African Union heads of state urging them to recommend Habre's extradition to Belgium.