Italian law Professor Luigi Condorelli, who is on the team of legal agents for Bosnia, quoted the declaration which Serbia-Montenegro's Council of Ministers adopted last July.
The declaration reads that "those who committed killings in Srebrenica and who ordered and organised that massacre represented neither Serbia nor Montenegro but an undemocratic regime of terror and death".
Condorelli said that such a statement constituted concrete admission that the previous government had masterminded the Srebrenica massacre in which about 8,000 local Bosnian Muslim (Bosniak) men and boys were killed when Serb forces in mid-July 1995 overran that area, which was at the time a UN safe haven.
The International Criminal Tribunal for the former Yugoslavia (ICTY) has qualified the 1995 Srebrenica atrocities in its rulings as genocide.
In the 2005 declaration, the government in Belgrade condemned the massacre and those who had organised it, including representatives of the previous government, Condorelli told a 15-member ICJ panel of judges, explaining that the state should be held responsible for those crimes according to the principle of continuity.
On Wednesday, representatives of Serbia-Montenegro will start presenting their arguments before this international judicial institution based in The Hague.