Okah is accused of masterminding two car bombings in Abuja, Nigeria on October 1, the country’s Independence Day, in 2010.
Twelve people were killed and 36 were injured. He was arrested in Johannesburg the following day.
Okah was allegedly the leader of the Movement for the Emancipation of the Niger Delta (Mend), that claimed responsibility for the blasts.
He was charged with engaging in terrorist activities, conspiracy to engage in terrorist activity, and delivering, placing, and detonating an explosive device.
Okah also faces terrorism charges over two explosions in March 2010 in the southern Nigerian city of Warri.
Nigeria’s minister of the Niger Delta, Godsday Orubebe, who was first to give evidence at the opening of Okah’s trial on October 1, 2012, said Okah was a “key figure in the Niger Delta struggle and the militants had a lot of respect for him”.
Okah has denied involvement in the attacks, which were claimed by MEND militants, and also denies being the leader of the group, which is fighting for a greater share of the Delta region’s oil wealth.
South Africa is trying Okah as part of its international obligations because Nigerian authorities have not applied for his extradition, according to the prosecution.