NDJAMÉNA, Chad -- "It took 24 years, but I finally got to face down the man who threw me in prison” said Souleymane Guengueng with a big grin outside the courthouse in this dusty capital. “He couldn’t even deny what he did.”Guengueng, who barely survived two-and-a-half years of mistreatment in the dungeons of former dictator of Chad, Hissène Habré, swore that if he got out alive he would bring his jailers to justice. When Habré was overthrown in 1990 by the current president, Idriss Déby Itno, and fled across the continent to Senegal, Guengueng rallied wary survivors and widows to his quest for justice. Twenty-one officials of Habré’s political police – the dreaded DDS - are now standing trial here, while Habré himself is in pre-trial detention in Dakar, Senegal.Habré’s government is accused of thousands of political killings and systematic torture. But it took two decades of campaigning by the victims before Senegal and the African Union established special chambers in 2013 to try crimes committed under Habré.