Four members of the notorious Serbian paramilitary group known as the Scorpions were convicted yesterday of murdering civilians after the fall of Srebrenica, in Bosnia, in July 1995.

The landmark trial — based on videotape made by the attackers that caused outrage when it was broadcast in 2005 — was the first in Serbia relating to the massacre of 8,000 Muslim men and boys seized from a “UN safe area”.

Five of the Scorpions, who were filmed laughing and mocking their prisoners before they killed them, were charged with war crimes. Four were convicted and a fifth was acquitted. Slobodan Medic, the commander of the Scorpions, and Branislav Medic, his aide, were sentenced to 20 years in prison. Pero Petrasevic, the only defendant to plead guilty, was sentenced to 13 years, while a fourth man received five years.

Judge Gordana Bozilovic-Petrovic told a packed court-room: “By committing such acts against defenceless civilians, by showing off their power and showing no remorse, the defendants gave the court no option of milder sentences.” The videotape of the killings was broadcast repeatedly and caused a wave of revulsion. Until then many Serbs had dismissed the accounts of the Srebrenica massacre as propaganda. All copies of the tape were believed to have been destroyed, but the last remaining one was tracked down by Natasa Kandic, a Serb human rights activist, who released it.

The footage was shown at the war crimes trial of Slobodan Milosevic, the late Serbian President, in June 2005. Ms Kandic said yesterday: “Considering the gravity of the crime, the ruling did not deliver justice.” The murders took place on July 17, 1995, in Trnovo, southeast Bosnia, during the same week that Bosnian Serb soldiers massacred up to 8,000 Muslim men and boys.

The video footage, parts of which can be viewed on the internet, recalls the work of the Nazi film units who recorded the Einsatzgruppen, the SS extermination squads, as they murdered Jews on the eastern front during the Second World War.

The footage is a chilling window into the aftermath of the fall of Srebrenica and the cold ruthlessness with which the Serb troops murdered their terrified captives. Burly paramilitaries drag thin and cowed Muslim men from trucks. One mocks a teenage boy that he will never have sex. The Serb troops clearly never imagine that one day they will be called to account for what they are about to do.

The prisoners have their hands tied behind their backs and show signs of being severely beaten. They shuffle along the road in the hot summer sun, surely aware that these are their last moments. One by one they are marched to the side of the road, told to stand and then shot in the back. One man twitches several times before he lies still. Two prisoners are kept back, including Azmir Alispahic, a 16-year-old boy who wanted to be a doctor.

The Serbs untie Azmir and another prisoner and order them to pick up the corpses. The cameraman urges the others to hurry up because the battery is dying. He pans around the executioners: they are pleased with their morning’s work as the smoke drifts from the muzzle of their guns. Azmir’s turn is next. In his last moments he turns and looks at the camera, as if pleading for help. It never comes.

His mother, Nura, attended the court hearing yesterday, one of several relatives brought from Bosnia under heavy police protection. She condemned the ruling: “This is an injustice. They brought them here to kill children and now they freed one and gave another five years.” Vladimir Vukcevic, the chief Serbian war crimes prosecutor, said that he would appeal against the lower sentences and the acquittal.

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