The UN Yugoslav war crimes court Tuesday quashed the acquittals of two top figures from the late Slobodan Milosevic's regime, ordering them to be retried on charges of running Serbian death squads in the 1990s.
There had been a storm of protest when Milosevic's former intelligence chief Jovica Stanisic and his deputy Franko Simatovic were acquitted in 2013 of five charges of war crimes and crimes against humanity.
But granting the prosecution's appeal against the acquittals, judge Fausto Pocar said the two men must be "retried on all counts of the indictment".
He said the original trial judges from the International Criminal Tribunal for the former Yugoslavia (ICTY) had "erred" on several points of the law.
Stanisic and Simatovic, both 65, were acquitted of the charges stemming from the brutal Balkan wars which erupted following the break-up of the former Yugoslavia in 1991.
More than 100,000 people died and some 2.2 million others were made homeless during the conflicts.
Prosecutors accused the two men of organising, financing and supplying Serb paramilitary groups, including an elite unit called the "Red Berets" and the feared paramilitary outfit run by Zeljko "Arkan" Raznatovic, called "Arkan's Tigers, between April 1991 and the end of 1995.
These units cut a swathe of terror and destruction across Croatia and Bosnia as they attacked towns and murdered Croats, Muslims and other non-Serbs to force them out of large areas in a bid to create a Serb-run state, prosecutors said.
UN prosecutors also alleged that Stanisic and Simatovic were part of a joint criminal enterprise, which also included late Serbian strongman Milosevic and Bosnian Serb leader Radovan Karadzic.
The ICTY's trial judges said in May 2013 that although the Serbian units carried out the killings, Stanisic and Simatovic could not be held criminally responsible, as they did not give the units specific orders to commit the crimes.
Trial judges also said there was not enough evidence linking the men to a joint criminal enterprise.
The appeals judges disagreed.
"The appeals chamber... finds that the trial chamber erred in law in requiring that the acts of the aidor and abettor be specifically directed to assist the commission of a crime," Judge Pocar said.
"The appeals chamber orders that Stanisic and Simatovic be retried on all counts of the indictment," he said.
Dressed in charcoal suits, both men listened without emotion as the judge read out the ruling.
They will now go back into ICTY custody pending the retrial, but judges did not say when the case will start again.
Milosevic himself died in 2006 while in the custody of the ICTY where he was on trial for war crimes, crimes against humanity and genocide.