Five former members of a Serbian police unit called the Scorpions have gone on trial in Belgrade for their alleged part in the 1995 Srebrenica massacre.
They are the first Serbs to be tried by a Serbian court over the massacre, the worst atrocity in Europe since 1945.
It is claimed the men are those who appear in a video shown at the trial of Slobodan Milosevic, in which six Bosnian Muslims are shot in the back.
It is alleged the men filmed the video of the incident themselves.
Relatives of the victims from Srebrenica attended the opening of the trial, as did relatives of the defendants.
The video - which lasts about 20 minutes - shows several members of the "Scorpions" police unit ordering six Muslim prisoners, dressed in civilian clothes, from the back of a lorry.
The victims are then marched into woodland and shot one by one.
They were among about 8,000 Muslim men and boys killed during the massacre at Srebrenica, when the town fell to Bosnian Serb forces near the end of the Bosnian war.
The men in court were arrested in June, just days after the footage was shown at the Milosevic trial.
The five accused men are Slobodan Medic, Pero Petrasevic, Aleksandar Medic, Branislav Medic and Aleksandar Vukov.
They face up to 40 years in jail if found guilty.
"There is no death sentence, but I hope justice will be served for those monsters," said Sajma Saltic, whose brother Sadik, 36, was among the victims identified on the video.
A sixth suspect has already been on trial for war crimes in Croatia, while a seventh has not been found.
Both the former Bosnian Serb leader Radovan Karadzic and his military counterpart, Ratko Mladic, are accused by the international war crimes tribunal in The Hague of orchestrating genocide at Srebrenica.
They remain Europe's two most wanted fugitives and are considered heroes by Serb nationalists, says the BBC's Matt Prodger in Belgrade.
He says the video, broadcast on Serbian television, shocked a nation which still believes, to a large extent, that Serbs were the principal victims and not perpetrators of the Balkan wars.
Next year the tribunal in The Hague is due to put nine former Bosnian Serb officers on trial jointly for the Srebrenica massacre. Eight of them are in the tribunal's custody.