The war crimes court in Bosnia-Hercegovina has begun its first genocide trial in the capital Sarajevo.
Almost 8,000 men and boys died in the Srebrenica massacre
Eleven Bosnian Serbs are accused of killing more than 1,000 Muslim men and boys in a single day during the July 1995 massacre at Srebrenica.
The group, of which 10 are former policemen and one a former soldier, have pleaded not guilty.
The court was set up last year to relieve the burden on the international tribunal in The Hague.
It has international judges and prosecutors.
Defendants include Milos Stupar, 42, a special police squad commander.
They face between 10 and 45 years in jail if convicted.
Prosecutors say the accused machine-gunned and threw grenades at prisoners trying to leave what was supposed to be a UN safe haven when it was overrun by Bosnian Serb forces.
"The prosecution will ask the court to declare these men guilty so that a small step towards meeting justice can be made," prosecutor Ibro Bulic said in his opening remarks, quoted by Reuters news agency.
During the week-long killing spree in and around Srebrenica, nearly 8,000 Muslim men and boys were killed, the worst atrocity in Europe since World War II.
The main figures indicted over the Srebrenica massacre, former Bosnian Serb leader Radovan Karadzic and former Bosnian Serb military commander Ratko Mladic, remain at large.