Speaking before Belgrade's Special Tribunal for War Crimes, Petrasevic said that Medic, who had pleaded not guilty, "should be ashamed for hiding behind the backs of (the other four accused)".
Petrasevic said that Medic had been ordered to kill the captives but could not name the man who had issued the order. "I was seeing the man I believe issued the order but I don't know who he is," he explained.
Petrasevic said he was "almost certain" he had personally killed one of the six captives and that he had "personally chosen the meadow" in which four were killed. He added he had not been present when the remaining two were killed in a nearby country house.
The defendant went on to say that the Scorpions unit had two stains, Trnovo in 1995 and Podujevo, Kosovo, in 1999, when 14 people were killed, of whom seven children, and five were wounded. He voiced hope that his testimony would help shed light on who had killed because they wanted to and who because they had to.
The other accused in the case, Aleksandar Vukov, Aleksandar Medic and Branislav Medic, pleaded not guilty of the Trnovo crime.
The indictment also accuses Milorad Momic, another Scorpions member who is at large, while Slobodan Davidovic, the eighth killer in a video recording of the crime which the public saw last year, was recently sentenced to 20 years in jail by the Zagreb County Court.
The trial in Belgrade resumes on Wednesday.