By Tamara Kovacevic
BBC foreign affairs analyst
Six Serbs are being tried in Serbia for their alleged involvement in the massacre of more than 200 Croat civilians in Vukovar in 1991. But in the Netherlands, three Serb officers - known as the Vukovar three - have been indicted by The Hague war crimes tribunal for their alleged role in the killings and are awaiting trial. Here is an outline of the tribunal's case against them:
Mile Mrksic, a Serb born in Croatia in 1947, was a colonel in the Yugoslav army when the conflict between the Croats and the ethnic Serbs broke out in 1991.
After a referendum, Croatia declared independence in June 1991. The Serb minority living in the country started an armed insurrection against the new nationalist Croatian authorities.
Mrksic surrendered to the tribunal in 2002
The Yugoslav army intervened on the side of the Serbs and the conflict escalated.
The charges against Mr Mrksic and his co-accused, Veselin Sljivancanin and Miroslav Radic, relate to the period after the fall of Vukovar, the Croatia city on the border with Serbia.
In late August 1991, the Yugoslav army surrounded the town, attacking it with heavy artillery and killing hundreds of people.
Croatian forces within Vukovar surrendered on 18 November 1991 and the Yugoslav army and Serb paramilitaries occupied the city.
On 19 November, Yugoslav army units arrived at Vukovar Hospital.
There, several hundred Croats and other non-Serbs sought refuge in the last days of the siege, in belief they would be evacuated in the presence of international observers, as agreed in negotiations between the Yugoslav army and the Croatian authorities in the capital Zagreb.
Instead, on 20 November about 300 men were loaded onto buses, driven to the nearby Ovcara farm and beaten by the soldiers for several hours. At least two men died from the beatings. Some of the captives were then released.
The others were then divided into groups and transported to a field where they were shot and killed.
Of the 300 people taken from Vukovar hospital, at least 200 were killed at Ovcara farm. More than 50 others are missing.
Mile Mrksic was in charge of the Yugoslav army unit which attacked and subsequently occupied Vukovar.
According to the indictment, together with his co-accused, Mile Mrksic commanded and supervised the soldiers who committed the killings at Ovcara.
After the siege of Vukovar, Mile Mrksic was promoted to general and later became the commanding officer of the army of a self-declared Serb autonomous region within Croatia.
After the Croatian forces overtook the region in August 1995, he retired from military service.
In May 2002, Mile Mrskic flew to the Netherlands to surrender to the UN war crimes tribunal.
The Hague Tribunal charges him with grave breaches of the Geneva Conventions - wilfully causing great suffering and wilful killing, two counts of violations of the laws or customs of law, cruel treatment and murder, and one count of crimes against humanity.
Veselin Sljivancanin was born in 1953 near Zabljak in Montenegro.
He was a major in the Yugoslav army and the operational commander for the Yugoslav army in the latter stages of the siege of Vukovar. He was subordinate to Colonel Mrksic.
Sljivancanin: Arrested in 2003
The day after the Yugoslav army took control of the Vukovar Hospital, Major Sljivancanin ordered nurses and doctors to assemble for a meeting.
While the meeting was taking place, the soldiers removed about 300 people from the hospital, among them wounded patients, hospital staff, soldiers who were defending the city, Croatian political activists and other civilians who sought refuge in the hospital.
They were taken to the Ovcara farm and at least 200 killed.
After Vukovar, Mr Sljivancanin was promoted to the rank of colonel and placed in command of a brigade in Podgorica, the capital of Montenegro.
The war crimes tribunal holds Mr Sljivancanin responsible for the same crimes as his commander Mile Mrksic - beatings and killings at the Ovcara farm.
Before the law on war crimes was passed in Yugoslavia, the Yugoslav press reported that Mr Sljivancanin always carried a hand grenade in his pocket. "I'll blow myself up if they approach me," he was quoted as saying.
He was arrested by security forces in Belgrade in June 2003 after a 10-hour stand-off between police and his die-hard supporters and handed over to The Hague tribunal.
Miroslav Radic was a captain in the Yugoslav army and in charge of a special infantry unit of the brigade which took an active role in the siege and capture of the city of Vukovar.
He was a close associate of Major Sljivancanin.
Radic: Gave himself up in 2002
According to the indictment, Mr Radic, together with Mr Mrksic and Mr Sljivancanin commanded and supervised the troops which shot and killed 200 people taken from Vukovar hospital on 20 November 1991.
The Hague tribunal charges him with the same counts of crimes against humanity, violations of the laws or customs of law and grave breaches of the Geneva Conventions for his role in beatings and killings at the Ovcara farm.
After Vukovar, Mr Radic left military service and entered into a private business in Serbia.
He gave himself up to the war crimes tribunal in 2002.