A casual visitor to the drab committee room in the British Parliament building where the fate of General Augusto Pinochet was decided during five weeks in 1998 and 1999 might have been excused for missing the case's historical significance. The law lords in business suits sat in front of robed and wigged barristers. Cartons of legal materials were piled high on chairs and tables. Most of the audience couldn't even see their lordships, much less understand their endless questioning about the finer points of British statutes and international conventions.

Yet human rights law came of age in that room. Not only were lofty proclamations like the United Nations Convention against Torture being applied concretely for the first time, they were being applied in the case of the man who symbolised ruthless dictatorship.

The lords' decisions that Pinochet did not enjoy immunity from arrest and extradition had an enormous impact on the development of an international legal system to redress repression.

Until recently, it seemed that if you killed one person, you went to jail, but if you had the power to murder thousands, you also had the power to arrange or impose your immunity, as Pinochet did in Chile. The Nuremberg trials established the legal principle that there should be no immunity for perpetrators of the gravest outrages, no matter who they are or where their crimes were committed. That principle was enshrined in United Nations conventions and the treaty of the new International Criminal Court (ICC). Yet until Pinochet's arrest in October 1998, few states had the courage to put these noble principles into practice.

The arrest of Pinochet, who died of a heart attack last week in Chile, inspired others to bring their tormentors to justice, particularly in Latin America, where victims challenged the transitional arrangements of the 1980s and 1990s that allowed perpetrators of atrocities to go unpunished and, often, to remain in power. Argentina's Supreme Court last year struck down immunity laws for former officials, and dozens face investigation and trial for crimes during the 1976-83 dictatorship. On November 17, Juan Maria Bordaberry, the dictator of Uruguay from 1973-76, was arrested for the murder of opposition leaders.

Pinochet's London arrest also strengthened a new international movement to end impunity for the worst abuses. After the creation of UN tribunals for Yugoslavia and Rwanda, the UN established the ICC to prosecute genocide, crimes against humanity and serious war crimes.

"International justice" is on the march in Africa. At the urging of the African Union, Senegal has finally agreed to prosecute the exiled ex-dictator of Chad, Hissène Habré, known as the "African Pinochet". Earlier this year, Charles Taylor of Liberia was handed over for trial for war crimes to the UN-backed Special Court for Sierra Leone by Nigerian President Olusegun Obasanjo. The ICC is now investigating alleged crimes in Darfur, Uganda and the Democratic Republic of Congo.

Yet the final frontier has yet to be breached. Up until now, Western leaders have seemed immune from international justice. The most important test case now under way is a complaint filed last month in Germany against former US defence secretary Donald Rumsfeld and others for alleged war crimes at Guantánamo and Abu Ghraib. Rumsfeld's role in approving the use of illegal interrogation techniques such as "waterboarding" and the terrorising of detainees with guard dogs is no longer in doubt. Germany's handling of the Rumsfeld case will tell us whether the "Pinochet precedent" applies to the leaders of powerful nations as well as weak ones.

As for Pinochet himself, his arrest in London unleashed a renewed debate in Chile about the legacy of the military government. When he returned to Chile, he faced dozens of criminal charges. His immunity was stripped in six major cases, from death squads and abductions to the hiding of millions of dollars abroad, and, at the time of his death, he was under house arrest and profoundly discredited in his own country.

Pinochet may have died without standing trial, but justice caught up to him in every other sense.