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, 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'.