Lagos - Supporters of the activist Ken Saro-Wiwa on Tuesday marked the 20th anniversary of his execution as the country's main human rights body called for a posthumous pardon.
Saro-Wiwa was hanged after a three-member tribunal convicted him and eight of his colleagues in a secret trial over their alleged involvement in the killing of four prominent chiefs in the Ogoniland region of southern Nigeria.
He always denied involvement and the executions on November 10, 1995 triggered an international outcry and sanctions against Nigeria, including a four-year suspension from the Commonwealth.
Several days of celebrations, including church services, poetry readings, music concerts and candlelit processions, culminated in a memorial rally in Ogoniland's main town of Bori on Tuesday.
But many in the oil-rich Niger Delta region, where farming and fishing have been hit by repeated spills, say the concerns Saro-Wiwa highlighted have gone unaddressed in the last two decades.
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"Government has done little or nothing to assuage the sufferings of the Ogoni people or address their complaints," said Ledum Mitee, who was Saro-Wiwa's deputy in the Movement for the Survival of the Ogoni People (MOSOP).
A 2011 UN environment agency report recommended that the Nigerian government and oil giant Shell clean-up Ogoniland but last week rights groups said both had still failed to act.
"Even after the execution, the poverty level in Ogoniland is still high," Mitee, who was acquitted at the 1995 trial, told AFP.
"People still... face challenges of water, decent living and environmental pollution, devastation of farmland and gas flaring."
Amnesty International's Nigeria director M.K. Ibrahim described the lack of development in 20 years as a "heartbreaking tragedy".
The secret trial and conviction of Saro-Wiwa and his colleagues and the failure to allow an appeal led to calls of "judicial murder" against Nigeria's then-military regime headed by Sani Abacha.
A retired army colonel, Hammed Ali, sat on the tribunal. President Muhammadu Buhari recently appointed him head of customs.
On Tuesday, the head of the Nigerian Human Rights Commission, Chidi Odinkalu, said it was beyond doubt the trial was "deeply flawed" and "unsafe" as due process was not followed.
Confirmation of the verdict should have gone to the Armed Forces Ruling Council, the ruling junta, for consideration before capital punishment was carried out, he said in an email.
A posthumous pardon for the writer and environmental activist was the only way to restore the integrity of the state that "breached its own laws to procure a killing", he added.
Britain's The Guardian newspaper last week said a memorial sculpture of a bus inscribed with the words "I accuse the oil companies of..." was sent as a gift to mark the anniversary of the execution.
But customs officials in Lagos refused to release it, citing its "political value".
In Bori, Mitee described the 20th anniversary as one of "sober reflection", not only for his colleagues but his own brush with death.
"I attended the candlelight procession for the late heroes yesterday night (Monday). I am keeping to myself today to reflect on my life and the struggle," he added.
For Hossanna Kpniem, an Ogoni activist, the daily struggle has hit the campaign for development in the region.
"Primary to me now is the fight to fill my stomach," she said.
Saatah Nubari, another Ogoni activist, blamed the current leaders of Ogoniland for failing to build on Saro-Wiwa's struggle.