THE HAGUE — Embarrassed by its failure to prevent Europe’s worst atrocities since World War II, the United Nations Security Council created a tribunal in 1993 to track down and punish those responsible for the horrific violence against civilians that convulsed the Balkans during the breakup of Yugoslavia.
Over its 24-year life, the tribunal indicted 161 people, heard from nearly 5,000 witnesses and met for 10,800 days. It convicted people from all parties to the conflict on war crimes and crimes against humanity, though the largest number were Serbs. Six Bosnian Serbs, including the political leader Radovan Karadzic and the military commander Ratko Mladic, were convicted of genocide and sentenced to lengthy prison terms.
Its pioneering work, televised from the court, introduced a new vocabulary into the public realm. Terms like ethnic cleansing and “mass rape as a weapon to destroy lives,” notions once confined to experts, are now widely used.
As the tribunal expanded the body of international law that had lain mostly dormant since the trials at Nuremberg and Tokyo after World War II, it spawned an avalanche of scholarship.
Other courts followed it, dealing with Rwanda, Sierra Leone, Cambodia and Lebanon. Many believe the tribunal provided the momentum for the founding of the permanent International Criminal Court.
But at a closing ceremony this past week for the court, known as the International Criminal Tribunal for the Former Yugoslavia, the mood was sober.
The United Nations secretary general, António Guterres, said that “accountability has taken root in our collective consciousness.” But international criminal justice, he said, was still a “long-term undertaking.”
Speaking in the medieval Knights Hall in the presence of the Dutch king, Willem-Alexander, Serge Brammertz, the tribunal’s chief prosecutor, said: “It seems as if today, there are more conflicts than in recent history.” He added, “The need for justice is immense, but so are the political barriers.”
The ceremony had the tinge of a memorial service, as fragments from witnesses’ testimonies were displayed on a giant screen and an actress read out heartbreaking accounts from victims of atrocities. Some in the audience were moved to tears.
The tribunal first captured the world’s attention late one night in 2001, when a helicopter dropped the man who until then was Serbia’s president into the courtyard of the United Nations jail near The Hague. Slobodan Milosevic became the first former head of state to appear before a modern international war crimes court.
He died in prison of a heart attack in 2006, two months before his trial was due to end. Prosecutors were blamed for having been overly ambitious, bringing 66 charges covering three wars — in Croatia, Bosnia and Kosovo — which they said he had instigated.
The trial of Mr. Milosevic, though, revealed government archives and evidence that contributed to a different public mind-set. “When I was in law school, it was normal for dictators to retire in the south of France,” said Diane Orentlicher, a law professor at Washington’s American University. “All my students have grown up in a world where it’s normal to think a mastermind of atrocities must be brought to book.”
When the court was created, the wars of 1992-1995 still raging, its outlook was anything but rosy: It lacked money, administrative staff and investigators, and it faced tasks unlike anything prosecutors or defense lawyers had faced in national jurisdictions. Evidence was often hidden in secret mass graves, and witnesses had fled. Crime scenes were riddled with land mines.
“The office felt a bit like the Wild West,” said Michelle Jarvis, a deputy to the chief prosecutor, who joined in 1997 as an intern. She recalled being told that “everything we do all day, every day, is difficult, there’s no precedent, there are no straight answers.”
Without an armed police force of their own, tribunal detectives struggled to find fugitives or deliver arrest warrants; NATO peacekeepers initially said arrests were not part of their mandate.
Politics played a big part in getting fugitives to The Hague: The United States threatened to hold back aid to Serbia unless Mr. Milosevic was handed over. Senior Croat and Bosnian Serb defendants, including Mr. Karadzic and Mr. Mladic were finally delivered, apparently as a condition for European Union candidacy.
The first low-level offenders from Bosnia arriving in The Hague served as a testing ground for new rules and laws. Judges went for guidance to texts of modern international conventions that had never been applied in trials, and had to turn them into applicable laws.
“It all felt so urgent, so important,” recalled Douglas Stringer, a former American federal prosecutor who arrived in 1997. “People were watching closely to see if this court could fly or if it would crash and burn. It wasn’t clear; it was all an experiment.”
Failure was not an option for Antonio Cassese, a prominent Italian jurist and the court’s first president, who died in 2011. Several of his early decisions, initially seen as controversial, broadened basic precepts of international criminal law.
He wrote that war crimes could occur not only in wars between nations, but also in conflicts within a country. In another decision, he ruled that massacres, torture and other atrocities committed by a government or a group could constitute crimes against humanity, even without a war. “It was intended for tyrants abusing their own people,” he said in a later interview.
To tie politicians to the violent campaigns they had planned far from the scenes, judges came up with the doctrine of “joint criminal enterprise,” tantamount to the notion of conspiracy used against organized crime.
The tribunal, and its Rwanda counterpart, also created precedents on sexual crimes committed in times of conflict.
Judges at the Rwanda tribunal said rape could be prosecuted as part of genocide. The Yugoslavia tribunal, which received reports of more than 20,000 rapes in Bosnia, went further, ruling that systematic rape could also be treated as enslavement, torture and a weapon to destroy lives, and therefore as a war crime.
Ms. Jarvis, the prosecutor, said that of the 90 convictions at the Yugoslavia tribunal, more than half included responsibility for sexual abuse.
Critics insisted that the prosecution examine possible crimes by NATO for its bombing of civilian targets in Serbia. Investigators did, and later reported that civilians were killed, but that they received no cooperation from NATO and were unable to find war crimes.
The end of the tribunal’s life has made for more open debates around the normally secretive court. Defense lawyers said they had been treated as poor relatives, left without the much vaunted “equality of arms” and overwhelmed by the power of the prosecution.
Another sensitive issue involved the uneven quality of the judges. Close to half the tribunal’s judges, who were commonly backed by their governments and elected by the General Assembly of the United Nations, had been diplomats or academics without trial experience, causing delays and frustration at times.
Wolfgang Schomburg, a German judge formerly at the tribunal, said that only judges with courtroom experience should be admitted in any future war crimes court. “How can we justify that defense lawyers required seven years experience to appear before this tribunal, and judges none at all?” he asked.