Friday is the 30th anniversary of the deadliest massacre in Europe since World War II, when Bosnian Serb forces under Gen. Ratko Mladic overran an area meant to be protected by the United Nations. Soon after, they proceeded to execute more than 8,000 Bosnian Muslim men and boys.

The magnitude and audacity of the slaughter shocked the world and spurred international prosecutions, making it one of the rare times that a genocide has been prosecuted since the Holocaust. The International Criminal Tribunal for the former Yugoslavia indicted and took into custody 161 people. Some 90 were convicted, including Mr. Mladic and Radovan Karadzic, the Bosnian Serb political leader, both of them for crimes that included the genocide in Srebrenica.

The prosecutions played the important role of punishing and marginalizing these leaders, individualizing guilt in lieu of broad collective blame, reaffirming the rule of law and paying tribute to the victims.

But Srebrenica also illustrates the limits of the law, especially when societies fail to adequately acknowledge such atrocities and eliminate the hatred that led to them. That has lessons for other potential prosecutions for more recent and ongoing conflicts, from Gaza to eastern Democratic Republic of Congo.

Today, denial of the Srebrenica genocide is the shameful policy of Republika Srpska, the largely Serbian part of Bosnia and Herzegovina where the killings occurred. Convicted war criminals are publicly celebrated by some. A recent history curriculum for elementary schools portrayed Mr. Mladic and Mr. Karadzic as heroes and omitted their convictions. In neighboring Serbia, President Aleksandar Vucic also rejects the term “genocide,” despite the international tribunal’s convictions and a parallel ruling by the International Court of Justice.

The most powerful voices for truth have come from the Mothers of Srebrenica. These women, many of whom lost entire families in the massacre, have spent decades demanding a full accounting of what happened. They are still waiting for their society — and their neighbors — to acknowledge what was done to their loved ones. They face harassment and threats. Some are still waiting to bury their dead.