By Madjiasra Nako and Emma Farge
N'DJAMENA/DAKAR (Reuters) - More than 20 Chadian security agents appeared in a special court charged with murder and torture on Friday, at the start of the country's first trial linked to abuses during the rule of ousted strongman Hissene Habre in the 1980s.
Scores of people who said they had suffered at the hands Habre's secret police packed into the courtroom, some holding signs saying "No to Impunity" and "24 years of waiting".
Human rights groups hold Habre responsible for killing up to 40,000 people in the eight years he ruled the oil-rich central African state, before being overthrown by current President Idriss Deby in 1990.
Twenty-one defendants pleaded not guilty to the charges at their first appearance on Friday. Another four men on the charge sheet have since died, and four more were either ill or on the run, said court officials.
Among the defendants in the courtroom was Saleh Younous, former director of Chad's notorious secret police force known as the DDS. Rights groups have accused it of regularly torturing suspects in the capital's Camp Martyr prison.
"It is the start of relief to see these powerful men of yesterday standing before the judges," said Fatime Mando, one of the women packing the court, her voice trembling.
Another woman, who said she was raped by state officers during a repressive period known as "black September", told Reuters she feared the full truth would never come out.
"On Chadian soil, many things cannot be revealed for fear of denouncing other accomplices who now find themselves in a vulnerable position," she said.
Reed Brody of Human Rights Watch who has worked with Habre victims for more than a decade, said the trial was a historic event. "This could be Chad's Nuremberg if it's done properly," he said.
But he added he was worried the trial might be rushed through, possibly to ease public pressure on the government, which has been accused of failing to cooperate with a separate trial of Habre due to begin in Senegal next year.
The Senegal trial -- the first in which a former African head of state is charged with crimes against humanity by an African government -- has suffered delays and many legal sources have blamed the Chadian government.
Chad has refused to transfer two defendants to Senegal, where Habre fled after his overthrow, including a former DDS director.
Current President Idriss Deby was a military chief during Habre's time in power.
(Editing by Andrew Heavens)