The accused Slobodan Medic, Branislav Medic, Aleksandar Medic, Pero Petrasevic and Aleksandar Vukov, as well as unit members known as Misa Turcin, Bobo, and Djole Siptar, are charged with shooting dead six male Muslim prisoners near Trnovo in the Srebrenica area of eastern Bosnia on 16 or 17 July 1995.
The indictment was issued on 7 October this year after a gruesome video recording of the crime appeared in public.
"I did not commit the crime and I do not feel guilty," Aleksandar Medic told the judges. He said that four prisoners had been executed by Djole Siptar and two by Milorad Momic, who is on the run, but that the murders committed by Momic were not on the video recording.
The trial continues on Friday.