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."