By NICHOLAS WOOD and DAVID ROHDE
SARAJEVO, Bosnia and Herzegovina, July 7 - With as many as 50,000 people expected to gather in Bosnia on Monday to mark the 10th anniversary of the killing of at least 7,000 Muslim men and boys in the Srebrenica area during the Bosnian war, Western diplomats and military officials are struggling to explain why the two Bosnian Serb leaders indicted in the killings remain at large.
For close to a decade, Radovan Karadzic, the wartime leader of the Bosnian Serbs, and his military commander, Gen. Ratko Mladic, have evaded capture in a compact area - Bosnia is half the size of Kentucky.
They are regarded as the two most wanted people in Europe since the end of World War II. Both are accused of genocide for seeking to exterminate large parts of Bosnia's Muslim population during the civil war of 1992 to 1995.
The failure to capture either man, despite the presence of thousands of peacekeepers in the region, has prompted indignation from Bosnian survivors as well as war crimes prosecutors. "You have a military alliance in Europe whose job it was to do so," said Michael Johnson, the former chief prosecutor at the International Criminal Tribunal for the Former Yugoslavia, referring to NATO. "Why not?"
Mevludin Oric, who survived one of the mass executions at Srebrenica by hiding under his cousin's body for hours, said that as long as the two men remained free, the effort to prosecute war criminals in the Balkans would be a failure. "What kind of progress can it be when Karadzic and Mladic are still walking around 10 years later?" he said.
American and European commanders contend that they are getting closer to tracking down Dr. Karadzic and General Mladic and have carried out about 20 raids in the last six months on individuals and businesses suspected of helping war criminals hide. On Thursday, NATO forces detained Dr. Karadzic's son, Aleksander, on the ground that he had provided support to a war criminal, a spokesman said.
"It's terribly important to get these two guys, plus the others," said Douglas L. McElhany, the United States ambassador to Bosnia and Herzegovina. "This is the major reason things can't go faster, if only in terms of on-the-ground reconciliation between Croatians, Bosnians and Serbs," the country's three ethnic groups.
But war crimes investigators and some NATO officials say the hunt continues to be held back by a lack of detailed and accurate intelligence.
"Myself, I evaluate it was not enough intelligence," said Carla Del Ponte, the current chief prosecutor at the war crimes tribunal, which has charged both men with genocide. She said further support from the United States was essential to arresting Dr. Karadzic in particular.
A NATO official based in Bosnia said cooperation among the military intelligence agencies of the various countries involved in the peacekeeping operation was poor. "They do complain bitterly that no one put the pieces together," said the official, who spoke on condition of anonymity for fear of being reprimanded by his superiors.
Some Western diplomats contend that the best American intelligence assets have been focused on Iraq and Afghanistan and that private contractors have been used as part of the American intelligence-gathering operation in Bosnia.
"Their best assets are certainly not in Bosnia right now," said a European official who works closely with the international tribunal and who also spoke on condition of anonymity because he feared being reprimanded.
While hopes have risen recently that General Mladic, who is thought to be in Serbia, might surrender because of heightened political pressure on Serbian officials, which has led them to turn over a number of other men accused in the Srebrenica killings, there has been little headway on Dr. Karadzic.
The continued ability of Dr. Karadzic and General Mladic to remain at large is seen as holding back development in the countries formed by the breakup of Yugoslavia in the 1990's. American and European officials have made it clear that no country in the region will be allowed to join NATO or the European Union until they transfer all war crimes suspects to the tribunal, which is in The Hague.
The military effort to arrest the two men has been plagued by problems from the beginning. After 60,000 American and European troops were sent to Bosnia to enforce the Dayton peace agreement of 1995, Dr. Karadzic and General Mladic continued to move freely about the country. But divisions within NATO and fear of casualties ensured that no efforts were made to arrest them.
"At the beginning there was not the will to arrest them," Ms. Del Ponte said. "After, it changed a little bit, but it was a fear to have conflict - a confrontation with bodyguards, to have problems with soldiers, who could be killed."
While efforts were stepped up beginning in 1997, Dr. Karadzic showed little fear of being caught.
Copies of a half-dozen letters said to have been written by him, while in hiding, to his wife between April 2001 and December 2002 describe repeated visits by his wife and a planned visit with his daughter, both of whom have long been presumed to be under NATO surveillance.
The letters, which were seized by Western military forces and which war crimes investigators say they believe are authentic, were provided to The New York Times by an international official working to secure his arrest. Excerpts have also been published by Balkan and British news organizations.
In a letter dated June 21, 2002, a reference is made to NATO's seeming failure to realize that Dr. Karadzic's wife was visiting him. "They saw you before, but nobody made a connection before that you travel here and there," it says.
In a Sept. 6, 2002, letter he appears to caution her about the use of the telephone but said he was well protected. "Of course, caution is necessary," the letter says, "but there is no need for such fear and paranoia."
He also describes receiving phone calls, cards and gifts from his supporters and his wife. "The colored shirts are O.K., although they could be a little big," said a letter dated Dec. 18, 2002. "I also have sufficient socks for now."
About 7,000 peacekeeping troops remain in Bosnia, but in the last nine months, military officials and diplomats say, increased political pressure on Bosnia and on Serbia and Montenegro to cooperate with the tribunal has fundamentally changed the atmosphere.
Negotiation deadlines for Serbia to seek European Union membership and for Bosnia to join NATO have prompted the transfer of 23 war crimes suspects to The Hague in nine months. Both governments say they are working actively to turn General Mladic over to The Hague.
The European official who works closely with the tribunal said hopes for General Mladic's surrender were high, as he is thought to be hiding in Serbia, which wants to start negotiations for closer ties with the European Union. But there is little mention of Dr. Karadzic, whose whereabouts are unknown.
"Frankly, we don't expect much," the official said.