The International Criminal Tribunal for the former Yugoslavia, sitting in The Hague, Netherlands, heard a prosecutor list the atrocities allegedly committed by soldiers under Mladic's command as Bosnian Serb units carried out an ethnic cleansing during the Bosnian war in the 1990s and directed a reign of terror against the civilian population in Sarajevo, The New York Times reported.
CNN said the 70-year-old Mladic defiantly glared at survivors of the 1992-95 war in the court, at one point drawing his finger across his throat. Another time he growled.
Mladic is charged with 11 counts of genocide, war crimes and crimes against humanity. Bosnian Serb forces allegedly used gang rape as a weapon and forced some women to perform sex acts on members of their own families.
Among the counts listed in the indictment against Mladic was the siege of Sarajevo, a 44-month campaign of sniping and shelling in which more than 10,000 people died.
Mladic, captured in Serbia last May after 16 years on the run, faces two counts of genocide, one for the ethnic cleansing campaign and a second for overrunning a small contingent of Dutch U.N. peacekeepers in Srebrenica in July 1995. An unchecked massacre of some 8,000 unarmed men and boys followed over several days in what Bosnian Serbs described as acts of vengeance for Serbian deaths at the hands of Muslims.
"Victims have waited for nearly two decades to see Ratko Mladic in the dock," said Human Rights Watch senior counsel Param-Preet Singh. "His trial should lay to rest the notion that those accused of atrocity crimes can run out the clock on justice."
If convicted, Mladic could face a life sentence in a European prison.
The prosecution expects to call 411 witnesses, though much of their testimony has already been recorded and submitted in the trials of other Balkan warlords, the Times said.
Those warlords include Bosnian Serb wartime political leader Radovan Karadzic, a former psychiatrist arrested in 2008 for alleged war crimes committed against Bosnian Muslims and Bosnian Croats during the Siege of Sarajevo, as well as ordering the Srebrenica massacre, and former Serbian President Slobodan Milosevic, arrested in 2001 for alleged war crimes and crimes against humanity in the wars in Bosnia, Croatia and Kosovo. Milosevic died in detention in 2006, a few months before a verdict in his trial.
Mladic's trial is to be the last before the criminal tribunal disbands in 2014, after prosecuting the last fugitive from among the court's 161 indictments, most resulting in convictions, officials said.