Mr. Radovan Karadzic, one of the world's most-wanted war criminals, has been arrested. After a 13-year manhunt, Mr. Karadzic was found, living openly in Belgrade. The arrest is one more indication that there is no refuge for those who commit atrocities and crimes against humanity. It also validates Europe's strategy of reaching out to Serbia and using its not inconsiderable leverage to get Belgrade to cooperate and bring criminals to justice.

Mr. Karadzic is charged with masterminding mass killings of Bosnians during the breakup of Yugoslavia in 1992-1995. That vicious bloody struggle pitted ethnic Serbs against Muslims, Croats, and other non-Serb civilians in Bosnia and Herzegovina as that republic — one of six in the former state of Yugoslavia — fought for its independence. By war's end, some 250,000 people were killed and another 1.8 million forced from their homes. Mr. Karadzic was the leader of the Bosnian Serbs, and provided the public face for militias that engaged in ethnic cleansing to eliminate opposition to the annexation of parts of Bosnia by Serbia. Among other crimes, he is considered responsible for the 1995 massacre of 8,000 Muslims in Srebrenica, the worst mass killing in Europe since World War II. The indictment at the United Nations war crimes tribunal accuses Mr. Karadzic of genocide, extermination, murder, willful killing, deportation, inhumane acts and other crimes.

The first indictment of Mr. Karadzic was issued in 1995. But it was not until 1998 that he, along with other Bosnian Serb leaders, went underground as peace became a real possibility and he had to fear for his freedom. The Belgrade government has long been suspected of turning a blind eye to Mr. Karadzic. He was rumored to have been hiding in monasteries or living in caves.