In a historic courtroom reunion of the two alleged chief architects of Serb atrocities during Bosnia's 1992-95 war, Ratko Mladic was testifying under subpoena for his former political master, Radovan Karadzic.
Both men are on trial separately in The Hague for crimes including genocide. They both insist they are innocent.
Mr Karadzic's team said former Bosnian Serb army commander General Mladic was "the one person in the whole world who knows best what happened in the war in Bosnia."
Mr Mladic refused to testify, calling the tribunal a "satanic court."
Former Bosnian Serb army commander General Ratko Mladic condemned the United Nations' Yugoslav war crimes tribunal in the Netherlands as a "satanic court" as he began giving evidence as a defence witness for his former political master, Radovan Karadzic.
Ratko Mladic and Radovan Karadzic are facing charges for war crimes and crimes against humanity.
This is the first time they are appearing in public together since the end of the conflict in former Yugoslavia.
Mr Mladic's request not to testify due to poor health and possible prejudice was denied by the court.
As forensic teams continue to uncover bodies in a mass grave in northern Bosnia, one woman has said that she is still waiting for the bodies of her brother and husband.
Nasiha Klipic told ITV News: "I have come to this cemetery for many years and I see each and every one of these buried people as my brothers – as my family.
"But I would feel a lot better if my brother and my husband finally found their final resting place here."
However, she said that even if the bodies of her relatives were found she would not rest until all those responsible were held to account.
"It would not be the end for me, the end for me would be when all the war criminals are arrested.
"I will not stop until the day I die and I raise my children not to stop until the day they die, until all the war criminals are arrested. Nothing less than that would be the end for me."
It is hoped further evidence found at the huge grave site could help the trials of Ratko Mladic and Radovan Karadzic, who are currently facing charged at The Hague.
The discovery of a mass grave in northern Bosnia and Herzegovina has brought hope that more evidence could be found for the trial of Ratko Mladic and Radovan Karadzic who are facing trials at the War Crimes Tribunal in The Hague.
Eldar Jahic from the prosecutor's office has told ITV News that teams from The Hague have already visited the site.
A United Nations tribunal has reinstated a genocide charge against Radovan Karadzic for attacks on non-Serbs in 1992.
Radovan Karadzic, the former Bosnian Serb leader began his defence today, accused of genocide and war crimes in Bosnia during the 1990s.
He said far from being accused, he should be praised for his efforts to promote peace.
Prosecutors have accused him of responsibility for the shelling of the Bosnian capital when it was under siege by Bosnian Serb forces.
Former Bosnian Serb leader Radovan Karadzicwill begin his defence against charges of war crimes at The Hague.
He faces 10 charges including genocide, war crimes and crimes against humanity. He has denied the charges, which relate to the Bosnian war of the 1990s. Karadzic could face a maximum sentence of life in prison if convicted.