The chief prosecutor for the UN war crimes tribunal in The Hague says Europe's most wanted man, Radovan Karadzic, has "gone off the radar screen" and no one knows where he is.
There has been speculation for some time that a secret deal may have been done between Mr Karadzic - the Bosnian Serb wartime leader - and US officials at the end of the Bosnian War.
Now The Hague has asked prosecutors in Serbia to examine the claims. The BBC's Nick Hawton investigates.
In a restaurant in Belgrade, Vladimir Nadezdin greets me with a smile and offers me coffee.
Mr Holbrooke helped bring Milosevic to the 1995 Dayton talks
A former senior official in the government of ex-Yugoslav President Slobodan Milosevic, he says he saw a document relating to the deal, signed by Mr Karadzic and the American negotiator, Richard Holbrooke.
"It was in 1995, the meeting took place in the Serbian presidency," Mr Nadezdin tells me.
"The piece of paper was in A4 format with the official logo of the Bosnian Serb Republic [Republika Srpska] and the president of the republic," he says.
"The first point was about Mr Karadzic giving up his political functions, the second one was about his withdrawal from party functions.
"The third one was about the withdrawal from the public life, and the last one, which was the most important one, was that Radovan Karadzic would not be under the jurisdiction of The Hague," Mr Nadezdin says.
Richard Holbrooke was the chief US negotiator who, through a combination of cajoling and energetic shuttle diplomacy, helped bring the warring sides together to sign the Dayton peace agreement in December 1995, which ended the Bosnian War.
He had a reputation for hard negotiating and not always using orthodox methods.
But the document that Mr Nadezdin describes has never been produced.
I travelled across the mountains and to the town of Pale, where the Bosnian Serbs had their wartime headquarters.
I had arranged to meet Radovan Karadzic's daughter in the Jet Set restaurant. She described when her father allegedly told the family that he had made a deal.
Vladimir Nadezdin says he saw documentary evidence of a deal
"My father called us, members of the family, in his office, late in the evening, I think it was 18 July 1996, and told us that he finally made a deal and that now he didn't have to be worried about The Hague anymore," she says.
"My father is still keeping his part of the deal."
Supporters of Radovan Karadzic have said for a long time that a deal was done.
But now investigators at The Hague tribunal have asked Serbia's chief war crimes prosecutor to investigate the allegations.
A spokeswoman for the Hague prosecutor's office said they did not want to leave "any stone unturned" in their hunt for Mr Karadzic.
A number of people have already been interviewed and others will follow. The results of the inquiry will be made public.
But it is significant that The Hague itself does not appear to be ruling out the possibility of a deal.
No smoking gun
In a statement, Richard Holbrooke's office described the allegations of a deal as an "outrageous lie" and said he was "astonished that people would believe a war criminal over the word of the United States or people who brought peace to the Balkans".
Mr Karadzic remains at large despite an international manhunt
Dejan Anastasijevic, a senior journalist with Belgrade's Vreme magazine who has spent more than a decade reporting on war crimes, says: "Mr Holbrooke was ready to promise anything to the players of the Bosnian War, including Karadzic and Milosevic."
"I believe he did calm their fears about the tribunal in many ways, but I find it very difficult to believe he left any paper trail or that there was a written agreement.
"Maybe some kind of oral agreement was made. Milosevic had a very strong motive for showing this document while on trial in The Hague, but he never mentioned any such agreement or contract - although he did want Mr Holbrooke to appear as a witness.
"But if this document existed I can't imagine Milosevic didn't have a copy."
The arguments over a document or a verbal agreement between American officials and Mr Karadzic are likely to continue.
There are alleged eyewitness accounts, but no smoking gun has been found.
Radovan Karadzic remains on the run and only perhaps when he emerges from the shadows will more be known.
But there seems little prospect of that happening anytime soon.
Nick Hawton's report was broadcast on The World Tonight, BBC Radio 4, at 2200 BST on Thursday 25 October. You can listen again online at