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.
The war crimes trial of ex-Bosnian Serb commander General Ratko Mladic has been delayed by a judge in The Hague due to "errors" by prosecutors in disclosing evidence to defence lawyers.
Alphons Orie told the UN Yugoslav war crimes tribunal today he was delaying the case due to "significant disclosure errors" by prosecutors who are obliged to share all their evidence with Mladic's defence team.
He says judges are still analysing the "scope and full impact" of the error.
The second day of prosecution opening at the trial of former Bosnian Serb army chief Ratko Mladic will focus on the mass killings in Srebrenica in 1995.
The trial, which began on Wednesday, is being held at a war crimes court in The Hague.
General Mladic, who is 70, faces 11 war crime charges, including two genocide counts. He denies the charges. General Mladic was arrested in Serbia last year after 16 years on the run.
He is charged with genocide at Srebrenica, where 7,500 Muslim men and boys were killed in July 1995. He also faces charges over the 43-month siege of Sarajevo, from May 1992 to November 1995.
ITV News correspondent Paul Davies reported on the issue of Ratko Mladic's arrest warrant in 1996. Today the trial of the former Bosnian Serb general began at a war crimes court in The Hague. He faces 11 war crime charges, including two genocide counts. He denies all the charges.
Bosnian Serb general Ratko Mladic taunted Srebrenica survivors at the start of his trial for genocide, running his hand across his throat in a gesture of defiance to relatives of the worst massacre in Europe since World War Two.
Mladic, now 70, flashed a thumbs-up and clapped his hands as he entered the courtroom in The Hague, where he faces possible life imprisonment for allegedly leading the slaughter of 8,000 unarmed Muslim boys and men in Srebrenica in 1995.
Later, Mladic made eye contact with one of the Muslim women in the audience, running a hand across his throat, in a gesture that led Presiding judge Alphons Orie to hold a brief recess and order an end to "inappropriate interactions."