The trial of mercenaries in the Equatorial Guinea coup plot - allegedly involving Sir Mark Thatcher - was "grossly unfair" with "serious procedural flaws," according to Amnesty International.
Amnesty sent observers to the case in the capital Malabo, where 11 mercenaries and nine Equatorial Guinea nationals were last week sentenced to long prison terms.
"From the time of their arrest in March 2004, the fundamental rights of the accused were routinely violated," Amnesty said. "No evidence was presented in court to sustain the charges against the accused other than their statements, which the defendants said had been extracted under torture."
Amnesty went on to say that the men were only given access to a lawyer two days before the trial and were not given the prosecution's evidence against them. Their statements were also presented in Spanish without adequate translation.
They were held incommunicado, handcuffed and shackled 24 hours a day. The irons were not removed in court, constituting cruel and inhumane treatment.
Weapons produced in court were not found in the possession of the accused but were presented as examples of what the prosecution claimed they intended to buy in Zimbabwe.
Amnesty called for the allegations of torture to be investigated as a matter of urgency, and for those suspected of involvement to be brought to justice.
The prosecution was led by the Equatorial Guinea attorney general, who has gained permission from the South African courts to question Sir Mark about his alleged role as a financier of the coup plot. Sir Mark, who denies the charge, has appealed. He faces a hearing in Cape Town in April.