Chad: Inside a dictator's secret police

For the two decades that he has been free, Souleymane Guengueng has constantly relived the two years he spent in a Chadian prison, where he watched hundreds of cellmates die from torture and disease. Thrown in jail in 1988 for still-unknown reasons, the deeply religious civil servant took an oath before God: If he ever got out alive, he would bring his tormentors to justice.