A close aide to former Nigerian military ruler Sani Abacha has been acquitted of killing the wife of politician Moshood Abiola, after spending 14 years in prison.
Major Hamza al-Mustapha was sentenced last year to hang for ordering the killing of Kudirat Abiola.
She was shot dead in 1996, three years after the elections her husband is believed to have won.
Those elections were annulled and Abacha seized power.
He went on to become one of Nigeria's most notorious military rulers, accused of stealing billions of dollars from the oil-rich nation.
Abacha and Abiola both died in 1998, paving the way for the end of decades of military rule the following year.
The BBC's Tomi Oladipo in Lagos say that a huge crowd of Maj Mustapha's supporters cheered outside the courtroom following the news of his acquittal.
The appeal court ruled that the charges of murder and conspiracy had been politically motivated.
The lower court "did not evaluate the evidence placed before it as the court was out to convict the appellant [Mustapha] at all costs," Judge Rita Pemu said, according to the AFP news agency.
"There is no evidence linking the appellant with the offence. Therefore, the appellant is discharged and acquitted," she added.
Maj Mustapha's lawyers appealed in December 2012, condemning as an "injustice" the many years he had spent in detention during the much-delayed case.
The prosecution, however, plan to appeal to the Supreme Court.
One of Abacha's sons, Mohammed, was also accused of links to Mrs Abiola's killing but was cleared in 2002 after three years in detention.
After Abacha seized power, Abiola declared himself president and was charged with treason.
He died in detention in the presence of US officials - a month after Abacha died from a heart attack.