A South African court has convicted Nigerian national Henry Okah of charges related to "terrorism", including bombings that killed 12 people in the Nigerian capital, Abuja, on independence day 2010.
"I have come to the conclusion that the state proved beyond reasonable doubt the guilt of the accused," said Judge Neels Claassen, handing down the verdict in the South Gauteng High Court on Monday.
Okah was found guilty of masterminding attacks including twin car bombings that killed 12 people in Abuja on October 1, 2010 and two explosions in March 2010 in the southern Nigerian city of Warri, a major hub of the oil-rich Delta
He faces a life term at minimum when the court hands him the sentence between January 31 and February 1.
The armed Nigerian group, the Movement for the Emancipation of the Niger Delta (MEND), which in 2010 was a well-equipped group fighting for a greater share of the Delta oil wealth, claimed responsibility for the attacks.
Although Okah has denied leading MEND, saying he just sympathised with their goals, court documents referred to him as its leader.
"[MEND] has been known in the past to blow up or disrupt oil installations and pipelines in the oil rich Niger delta area," Al Jazeera's Haru Mutasa reporting from Johannesburg, said.
"They are also known to take a lot of foreign hostages and ask for ransom," she added.
Documentary evidence of his role in the group included handwritten notes by his wife.
MEND has a history of staging fierce attacks on oil facilities and kidnapped oil expatriate workers in Nigeria's oil-rich southern Delta.
He holds permanent residence in South Africa, but is known to have travelled back and forth between the two countries.
In 2009 he was freed from a jail in the central Nigerian city of Jos where he was being held for treason and gun-running.
His liberation came in the wake of an amnesty deal offered by the government to thousands of Delta fighters.
The court said he then left for South Africa, but returned to Nigeria in early 2010, sponsoring the purchase of cars which were modified to allow the fitting of explosive devices.
Eight months later the cars were used to bomb independence day festivities that were attended by several foreign heads of state, including South African President Jacob Zuma.
Okah have denied involvement in the Abuja blasts, saying the charges were politically motivated. He was also accused of being one of the spokesmen for MEND.