The landmark ruling by the Constitutional Court means the Truth and Reconciliation Commission can continue to offer an amnesty - and indemnity from criminal charges and civil claims - to torturers and murderers from the apartheid era if they come forward voluntarily, freely confess and can prove that their crimes were politically motivated.
The relatives of Mxenge and Biko were among five families to challenge the constitutionality of the Commission, which was set up by the Government of National Unity in order to uncover the truth about the apartheid years and heal a divided nation.
The families, whose relatives were all allegedly murdered by the government security forces, argued that the Commission was an instrument of political expediency and that its amnesty powers robbed them of a chance to obtain real justice through the criminal and civil courts.
They said the state was ignoring its obligation under international law to "criminalise, prosecute and punish war crimes and crimes against humanity". Instead, after a few tears and an apology to the relatives, the guilty men have walked free.
For the past three months, at emotional public hearings throughout the country, victims and perpetrators have told harrowing stories of brutality. In their unanimous ruling the 10 Constitutional Court judges said without an amnesty there would be a "disincentive for the disclosure of the truth".
Mosibudi Mangena, president of Azapo, the black power organisation which backed the court challenge, said yesterday that the families were "very sad" about the decision but that action in the international courts would be considered.
Biko's widow, Ntsiki, 49, said she was "very frustrated". In 1977 her husband, then the young leader of the black consciousness movement which had swept South Africa's townships, was almost beaten to death by police officers before being driven 700 miles to a jail in Pretoria where he then died.
Mxenge's brother, Churchill, was also bitterly disappointed. His brother, Griffiths, a civil rights lawyer, was stabbed 40 times and had his throat cut after stopping to help some men who pretended that their car had broken down.
Last week, after months of lobbying, Churchill Mxenge had the satisfaction of seeing Dirk Coetzee, a former security forces captain, being charged along with four others for his brother's murder. However, the Constitutional Court's judgment appears to undermine the chances of that case ever reaching the courts.
Mr Coetzee confessed in 1989 to playing a part in Mxenge's murder. But he was never charged. The South African government denied Mr Coetzee's allegations that Mxenge's murder and many others were carried out by government- backed hit squads.
Mr Coetzee defected to the ANC before making his confessions. He has since rejoined the security forces as an ANC appointee and applied months ago for amnesty. He was waiting for his submission to be considered when he was charged. He has warned that his predicament may prevent other security forces personnel from coming forward.
Yesterday's judgement opens the way for the Commission's amnesty committee to announce the findings of the applications it has already heard. This should clear up the uncertainty among the perpetrators of human rights crimes about the extent of the amnesty's provisions. So far the Commission has had a softly-softly approach to perpetrators of crimes and there has been widespread criticism that too few have come forward.
The gloves are likely to come off if the numbers do not rise. Perpetrators risk their names coming up at hearings and being ordered to appear before the Commission. Those who have to be coerced face prosecution in the criminal courts.
It is the second legal victory for the Commission. It won an appeal in the Supreme Court last month, which allowed it to name the perpetrators of human rights violations at public hearings without prior warning being given to the accused.
The latest challenge to the Commission had only a slim chance of success, as the establishment of the Commission and the amnesty provisions in particular were crucial components of South Africa's negotiated settlement.
The Commission has powers to compensate victims of crimes and their families, but with so many abuses to investigate, there are unlikely to be many cases of financial reparation.Reuse content