Former Bosnian Serb military commander Ratko Mladic helped orchestrate an ethnic cleaning campaign in Bosnia in the 1990s, a prosecutor said. A war crimes trial for Mladic began Wednesday at a tribunal in The Hague, Netherlands. He\'s facing 11 counts of war crimes against humanity allegedly committed during the war in the former Yugoslavia the 1990s. Prosecutor Dermot Groome said Mladic, as commanding general of Serb forces, orchestrated the 1995 massacre at Srebrenica and bombing campaigns in Sarajevo. By the time of the events in Srebrenica, the prosecutor said, Mladic and his forces were \"well-rehearsed in the craft of murder,\" the BBC reports. Mladic commanded Serbian forces in the 1992-95 war in Yugoslavia. He was wanted by the International Criminal Tribunal for the former Yugoslavia for genocide and war crimes. He was arrested in a village about 50 miles north of Belgrade last year. The international courts had blamed Serbia for delays in handing over the commander. His arrest was seen as an obstacle to Serbian plans to join the European Union. Mladic was prone to outbursts during the opening day at The Hague. He\'s considered a national hero by some of his supporters. He says the charges against him are \"monstrous\" and a not-guilty plea was entered on his behalf.