Gaston said he is willing to testify before the grand jury if it will help get to the truth.

CNN: STORY HIGHLIGHTS

He appeared before the Truth and Reconciliation Commission last July to testify about his alleged role as architect of the apartheid government's covert chemical-and biological-warfare programme.

ECONOMIST: South Africa

Several other key witnesses, including the president of Chad's truth commission, Mahamat Hassan Abakar, are also expected to testify.

BBC: Habre's lawyers try to halt trial