Serbia's President Boris Tadic has vowed to find those who helped to protect the war crimes suspect Ratko Mladic for 16 years.
Mr Tadic also said appeals by the family of the former Serbian general will not prevent his extradition to The Hague to stand trial.
The 69-year-old faces charges of genocide during the Bosnian War in the 1990s.
His legal team is to appeal a court order on Monday on health grounds.
Mr Tadic told the BBC: 'In the next few days, we'll have a completed picture of what happened in the past two-and-a-half years, even more, in the past 16 years. And, for us, that is going to be very, very important.'
Meanwhile, Mr Mladic has called for calm over his arrest, saying he did not want to be a 'cause of unrest' on the eve of a far-right rally in Belgrade.
'He is appealing to people to calm down, there should be no bloodshed, he does not want to be a cause of unrest,' his lawyer Milos Saljic said.
The appeal came a day ahead of a planned rally by the ultra-nationalist Serbian Radical Party, which has called on its supporters to protest tomorrow evening against Mr Mladic's arrest.
A judge ruled yesterday that Mr Mladic was fit to face international justice at the war crimes court, despite pleas from his son that he was too ill to be transferred.
His supporters maintain that Mr Mladic was not guilty of organising the mass killings in Srebrenica - the worst single atrocity in Europe since World War Two - and the 44-month siege of Sarajevo.
Elsewhere, the UN Security Council said last night that it welcomed the arrest of Mr Mladic.
'The members of the Security Council welcome the arrest on 26 May 2011 of Ratko Mladic,' said French envoy and current Security Council President Gerard Araud in a statement.
The members, he said, 'congratulate the Serbian authorities on the arrest, which is a clear demonstration of cooperation from the government of Serbia with the International Criminal Tribunal for the former Yugoslavia'.
The council members also 'share the hope that the detention and transfer of Ratko Mladic will help to bring the western Balkans region closer to reconciliation and to their European perspective,' said Mr Araud.